Metric vs Standard, Imperial or SAE - Wrenches, Sockets, Bolt Size Chart + Mechanic Math

How do you tell if a bolt or nut is standard or metric, and what size wrench or socket to use? The charts below show which are interchangeable between metric and standard, aka imperial or SAE (Society for Automotive Engineers), millimeters vs inches, and how they compare in thousandths of an inch.
When a metric and standard size are similar, it's best to use the smaller of the two sizes if it will fit your bolt. Less than .005" is not usually noticeable. Over .010" tighter may not fit.
View or download and print chart from our website (I keep one in my toolbox):
PDF: www.silkfromthehartz.com/SAE-...
JPG image: www.silkfromthehartz.com/imag...
Word document: www.silkfromthehartz.com/SAE-...
Word doc highlighted w/yellow: www.silkfromthehartz.com/SAE-...
Which vehicles are SAE, Metric, or Mixed?
US vehicles pre-1970: All SAE
US 1970 - 90's: Mixed SAE & Metric
US vehicles after 2000: All Metric
Foreign non-US vehicles: All Metric
How to read bolt heads to determine if a bolt is metric or SAE:
No Markings or mfg. initials: Uncertain, likely SAE grade 2
SAE grade 3 to 8: 1 to 6 Radial Lines; 307A, A325; Stainless: F593C or similar
Metric: A number; 2, 4, 6, 8.8, 10.9, 12.9; 8.8 = grade 5; Stainless: A2-70 or similar
Mechanic Math example: 5/8" SAE wrench: 5 ÷ 8 = .625 inches (decimal equivalent in inches)
16 mm Metric wrench: 1 mm = .0394 inches x 16 = .630 inches, so the 16 mm is 5 thousandths of an inch bigger than 5/16”, which is close enough. Since the 5/8" wrench or socket is a tiny bit smaller, it will fit tighter on the bolt or nut (whether it is metric or standard) and reduce the chance of stripping, so if it fits, I'd use the 5/8".

[@f-puppet4059]

I like how you spaced the SAE measurements in relation to the metric measurements, so that we can have an idea of just how much difference there is to them. Thank you very much. Just what I needed in my toolbox. I've printed and laminated a few of these cards thanks to you!

[@HartzHomestead]

Glad it's useful to you. I kept running into this situation, so I designed the chart to be as practical as possible.

[@maverickp-5138]

😮😮😮😮😮😮😮😮😮😮😮😮 1:07 😮😮 1:14 😮😮😮😮😮😮😮😮😮😮😮😮😮😮 1:35 😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮

[@lastking2114]

This video should be showed in schools! Thanks for making the chart readily available to print!

[@IDIturboDiesel]

There is a substitute for 15mm and that is 19/32 which some tool sets have.

[@tinamarie4875]

Thank you for the valuable information, plus I also appreciate that you go right to the point and not try to humor us withlame jokes or unnecessary silliness or annoying background music and etc. Keep up the good work!

[@HartzHomestead]

You're welcome! Well said. I've seen so many videos that waste a lot of time. I know how frustrating that can be, like, get to the point, people! Tell us what we need to know.

[@Prolific_Knives]

This is likely the best conversion chart that I have seen out there describing the similarities and differences between mm and sae sizes. Thank you sir.

[@adventurevin7600]

This us great! I downloaded and printed a few of the charts to give to friends. This helps a great deal when I need to hold an opposing nut attached to a bolt. You explain it so clear and in minimal time. Thanks for providing the chart!

[@HartzHomestead]

Glad I could help! I use this chart myself quite a bit. Very handy.

[@growthmindset6549]

Thank you for such a comprehensive video! Just learned so much. Keep up the good quality videos!!

[@dandannoodle19]

never had to work with standard, this similar comparison of metric sizes to standard helped me place the sizes better in my head as I will begin working with SAE. TY so much for the video and the image for later jogging

[@evarage57]

Thank you for making this video. I am a scottish mechanic and ive only ever worked with metric bolts and nuts. i am about to travel to germany to start a new job as a heavy equipment mechanicfor the US Army. This has helped alot!

[@HartzHomestead]

You're welcome! I've had a couple vehicles that have a mix of both metric and standard, so having that chart saves me a lot of time.

[@brandonr.5625]

Awesome working on that currently too :)

[@shtika]

Excellent chart. Downloaded , thank you. I do have 17/32 , 19/32, 21/32 and 25/32 sockets however never used them except for show and tell and bets with co-workers.

[@DennisRackers]

Thank you! Your table on interchangeability is the only such document I found in a quick search and it will save me from time and hassle of doing the math or trial-and-error with the wrenches. I found your table while looking for a way to reduce the number of wrenches I carry when I'm away from my garage tools.

[@JNC1973]

You my friend are a life saver. I've been trying to figure for days what kind of bolt I need to replace that held on my clutch pulley wheel on my mini bike and nobody could answer my question. Now after stumbling upon your video I need Metric cause it does say 8.8 on the bolt head. I learned something new today. :)

[@HartzHomestead]

I had to do some research myself in putting this video together and found it's very handy being able to read bolt heads. Glad it helped! I'm surprised actually at how many bolts in the US are now metric.

[@anocri]

Fantastic informative video. Didn't know the differences all these years, and glad to know the differences. Was using the wrenches based on the fit. The chart is awesome so I can dance between SAE and mm in an attempt to find the correct size wrench for a bolt.

[@HartzHomestead]

Thanks! I love practical information like this that makes it easier to do things.

[@sonicknives]

Thank you! Ive only used metric and soon will need to use standard tools for my new position. Many thanks!

[@sneakysnake109]

I downloaded it. Thank you for the chat and the video!

[@mysticjedi6730]

Thank you for this video. I will print off a chart like this and tape on all my tool boxes. Great idea

[@boshintang]

Most useful video I've seen in a very long time.

[@TheRAMBO9191]

Old video, but ima guna try n print this chart and laminate it.! Thank you so much. I'm 32 never learned tools but starting to get interested. Had tons of family in construction but by time I hit 12 most past away including my dad at 9. Rough childhood but I know I had better still than most out there. I'm guna try to watch this video over n over to get an idea in my head.

[@HartzHomestead]

If you have a printer, you should be able to download the chart and print it.

[@kimifan06]

on race cars we use the 7/16 and 11mm interchangeably on the bleeders screws

[@TheSkylark16]

Great video! I finally use my 38mm sockets for 1 1/2" since SAE tools are way more expensive in my country! It's only 0.1mm diff

[@HartzHomestead]

Especially with the larger sizes, they are almost interchangeable. The bigger you get, the less relative difference. Sorry, my chart didn't even go to 38 mm, but since 3/4" is almost exactly 19mm, doubling it we can see that 1.5" = 38mm.

[@thumbsup9208]

That's what I was looking for. Thanks for sharing

[@CristianHernandez-px9uz]

Very informative man… God bless you!!!💯

[@serenakoleno9338]

Great video. Saves us time and money. Thank you.

[@Sweshification]

This is sooooo helpful, Thank you!

[@SherryAdcox]

Thank you. I have not used these ranches much in my life. Now I am on my own and having to do work around the house. I am very confused. This helps a lot.

[@j.p.8095]

Sir you r the best, thanks for the charts! Great work

[@asdfnone1346]

I measured my lug nut at 17mm and bought 17mm metric socket, boom! it didn’t fit! I think 19mm might fit after this experienced. Thank you sir for this information!

[@norge696]

Go on tekton and pickup a master socket set. No skips at all!

[@toribenita_kyo]

It's possible to substitute a 13-mm wrench with a 1/2" one, but it's going to be roughly 0.3 mm oversize (1/2" is approximately 12.7 mm). Adjustable wrenches can be used with both metric and inch nuts and bolts, but you're going to be sacrificing strength (and durability) for adjustability.

[@HartzHomestead]

Good points. An adjustable wrench is more likely to slip a little if it takes a lot of torque and thus may damage the bolt head. Sometimes a 1/2" wrench will fit a 13 mm bolt very snugly, but a 13 mm wrench will be very loose on a 1/2" bolt.

[@michaelkulman7095]

Yes, people miss that some substitutions only work in one direction. When I was young few had metric sets and as foreign cars became more common we made these subsitutions and even picked up extra SAE wrenches in some sizes to file down the open end to fit some metric fasteners that didn't have a crossover. The smart ones marked them somehow. Done with double open end wrenches and combination wrenches where you might even cut off the ring end as it wasn't a match for the open end anymore. Now someone will say why not just buy metric? Well we had SAE already and it was cheaper to pickup some more SAE at a pawn shop or a garage sale than to buy new metric wrenches. When we did buy new or used metric sometimes we would just fill in the holes where there wasn't any good crossover.

[@ShawnWeekly]

Amazing. Thanks for this video.

[@PatJones82]

Great Video and thank you for the chart!! Very helpful. :)

[@ATrainAC]

Appreciate you for this tip. Very helpful.

[@patgarry493]

I needed this. Thank you.

[@mewyattt]

Thanks for this video! After watching this, I'm buying metric and supplementing in SAE.

[@HartzHomestead]

Good plan! You could have full sets of both, but Metric are most common these days, filling in with SAE that have no metric equivalent.

[@yuvipanda]

This was very helpful to me! Thank you

[@keyanoverona7103]

Great video. Thank you!

[@michaelkulman7095]

Excellent video! People miss that some substitutions only work in one direction. When I was young few had metric sets and as foreign cars became more common we made these subsitutions and even picked up extra SAE wrenches in some sizes to file down the open end to fit some metric fasteners that didn't have a crossover. The smart ones marked them somehow. Done with double open end wrenches and combination wrenches where you might even cut off the ring end as it wasn't a match for the open end anymore. Now someone will say why not just buy metric? Well we had SAE already and it was cheaper to pickup some more SAE at a pawn shop or a garage sale than to buy new metric wrenches. When we did buy new or used metric sometimes we would just fill in the holes where there wasn't any good crossover.

[@petemoore8923]

I love hearing stuff like that. I work in a fab shop that has a dinosaur toolbox that belonged to god knows who before we moved in. I dig in it all the time. A LOT of modified wrenches in it.

[@michaelkulman7095]

@@petemoore8923 Carry weight was also a factor for some as carrying a full set of sockets and wrenches in SAE and metric is a big deal. Later I bought a set of Metrinch to address that...

[@wondersteven]

It's amazing how much info you packed into just 4.5 minutes or the metric equivalent of 4:26. Thanks.

[@HartzHomestead]

Thank you, actually closer to 4.433...minutes. At least Metric and Standard time is the same. Imagine if a metric day had 10 hours of 100 minutes, made of 100 seconds each. Why divide a day into 24 hours of 60 minutes each, except it's always been that way.

[@Ronnieyotob]

Thanks for this info, and chart! Found out the hard way these aren’t 1-1 interchangeable 😖 one stripped caliper bolt later I won’t make that mistake again!

[@HWCapps]

Thank You I needed that

[@maddalab]

Great video both the quality and the narration. You should do more videoes.

[@HartzHomestead]

I agree, I should finish more videos. I have several partially done, but the editing is very time consuming, and life is busy. Also KZbin is unpredictable and I've put huge amounts of time into videos that barely get seen, which is discouraging. This one happened to hit on a topic a lot of people need.

[@maddalab]

@@HartzHomestead A family member of mine has a channel and has done a few videos and taken a course. The algorithm biases towards promoting content from channels that post regularly. Twice a week is what it seems to like the most I believe. But as you say the video editing does take a lot of time and results can be unpredictable. Good Luck tho.

[@lewischacon6009]

Loved the video very informative sir.

[@HGEntertainmentTV1]

Thanks for the info. Learned now..

[@NigeriaFunk]

MANY THANKS!

[@gfrank8331]

Ty for this video not everyone was taught this

[@seanjohn2381]

awesome thank you. I also printed out the pdf file to put in my tool box

[@AlRHORN]

Very useful, thank you

[@nelsonthekinger]

Thanks for the video!

[@tommurphy9278]

Thanks for the chart comes in handy.

[@HartzHomestead]

You're welcome! I agree, I made the chart for myself first, and use it quite a bit. Glad to share it with you.

[@hakimhlm4084]

thank you, you help a lot my friend 😇😊

[@ROMANEMPIRE69]

Thank you for this amazing and informative video. Based on what I just saw I’d rather go ahead and get SAE in addition to my metric set of sockets and wrenches. Trust me I’ve had my “fun” with nut and bolt slippage. I’d rather get the correct fit. Also because i enjoy my tools even it’s just to pull out my tool box and look at the shine. 😜

[@HartzHomestead]

It's pretty hard to get by in this world without a set of both, at least here in the US. As an example, my camper jack bolts are SAE, but the propane fridge is made in Sweden, so it's all metric.

[@far06c]

Great video!!! Thanks!!

[@CaLiRr-of6ur]

Thanks , that will be useful.

[@ValeriiAS]

very useful, tahnks!!

[@paulg444]

great video, are there any practical near equivalences between SAE bolt and thread pitch and metric thread pitch, for instance is 7/16-20 practically equivalent to M12-1.25 ?

[@HartzHomestead]

Perhaps someone else has a more knowledgeable answer, but in my experience if a thread pitch isn't identical it probably won't work in most applications.

[@paulg444]

@@HartzHomestead That is my experience too.

[@michaelrobinson2528]

Awesome Video. thanks

[@dutchleussink156]

Thank You Sir.

[@salvaged_wretch]

As a diy/handywoman new to this … it’s all so mind blowing. Seems like this could’ve all been simplified… but then, where’s the money in that ?? 😅 Great tutorial nonetheless.

[@HartzHomestead]

The problem is these 2 systems developed independent of each other, so they are unrelated, and all we can do now is figure how to convert them. Metric is about as simple as possible, but imperial was too ingrained in the US already.

[@GHE2005]

Great! Most helpful.

[@user-it6gd6uh7e]

this is great

[@snugzillal]

Hello was wondering if working on a Chevrolet vehicles if you can use Metric measurements without damaging the bolts

[@HartzHomestead]

American vehicles, including Chevrolet, have been almost all metric since the 1990's, so unless you have a 1980's or earlier, it's rare to find a bolt that's not metric.

[@Channelgiron]

Thank You! Sir!

[@xx9mmskeeterxx174]

I just want to bring to light that sure both a metric tool and standard tool might "fit" a bolt, nut, etc but its the one that fits tighter with less slack that is the correct tool.

[@michaelkulman7095]

Actually sometimes the substitution actually fits tighter...

[@Daniel198549]

Very helpful

[@lithunsaravanan2784]

Super explanation

[@wytchypu7412]

fantastic!!!

[@adrianotrack9258]

Good vídeo

[@VODZ]

Awesome!

[@STARBOYGODD]

great video

[@Jsantosishere]

THANK YOU DAD I never had!

[@rickyrichy5496]

Thank you

[@smartele3247]

thank you

[@InverJaze]

Pet hate on cars is having a mix of both metric and imperial. Sometimes though having both sets of tools, does help when rust has reduced the size of a bolt or nut head.

[@HartzHomestead]

It does complicate matters. Car makers seem to do whatever is easiest for them, not the mechanic who has to figure out how to fix it.

[@petersamodhar9527]

Please please, make a video on b. S. W. Spanners old and new types.i would be greatfull to you.thankyou.

[@HartzHomestead]

Sorry, that's not something I have any expertise on. The information must be available somewhere on the web.

[@cristianbautista3837]

I have a 91 honda crx Japanese do you know if i should use metric?

[@HartzHomestead]

Yes, I believe all Japanese cars are metric.

[@ernesto7506]

Thanks

[@TacticalCentral]

So does this work then when needing to buy a Metric bolt size but all they have is SAE?

[@HartzHomestead]

Probably not, because the threads will not match. It's possible it could work, but not likely. If you're buying both the bolt and nut in SAE, that could work. But not if you're threading into something that has metric threads, unless you first tap it out with an SAE tap.

[@jg1468]

Can I use metric sockets on standard bolts or will I need a standard sockets as well?

[@HartzHomestead]

Some sizes are interchangeable, others are not. You can get away with a complete metric set plus a few standard sizes that don't have good metric equivalents. The most important are 3/8", 1/2", 9/16", 11/16", 13/16" plus you might want 1/4", 1" and 1 1/8". If you run into standard very often, you might as well have both sets.

[@hoffmanxgunnar]

And this is why I bought a full metric cause you can use most metric on standard and not so many standards on metric so if you only get one get metric

[@jhonnyboy7946]

Thanks very usefull

[@rickeyezell9136]

1 3/4 sae versus what size mertic

[@Eve....747]

Hi, I've got a bolt 🔩 with a marking 8...does this mean a grade 8 bolt in strength, bit confused 😕, what I thought before than now watching this video...the bolt is for a YAMAHA xj900s diversion suspension bolt... as I'm searching the meanings, basically bolt has seized onto frame, so will have to cut suspension away, then leaving bits of bolt stuck to frame, hopefully thy just will pop out!? 🤔, after major surgery or will have to drill out....as it's like this video is showing spanner size, which probably is true in meaning, though is the 8 on the bolt also meaning grade 8 strength... Kind regards Pete... 👍

[@HartzHomestead]

A number like 8 on the head usually means it's metric. An 8.8 is equal to grade 5. An SAE grade 8 bolt would have 6 radial lines, so it's likely not that. Yamaha is probably all metric. Sounds like you might have to drill it out, or use a screw extractor. I assume you've already soaked it well in penetrating lubricant, used an impact wrench or hammered it a bit, and tried heating around it with a torch.

[@kingduckford]

I drive several 1980's Fords, so I must have a full set of each Metric and SAE. That said, my experience is ALWAYS use the proper socket and NEVER use one that is "close enough" because that IS how you strip stuffe. Better safe than sorry, because you know just how fun it is to take out a rounded head bolt....

[@1marcelfilms]

I wonder how well a 3/8 will do on a rusty rounded 10mm

[@ArtofSilkPainting]

If you can get it on there, maybe file the 10mm down flat on 2 sides, otherwise lubricant and vise grips.

[@gentlerowdy]

hi can you help us know the difference between sae & AF or they both are same ?

[@HartzHomestead]

AF simply means "across flats" so my understanding is a wrench marked AF could be either metric or standard. The AF doesn't really mean anything now days since all wrenches are marked with the distance from one flat to the parallel flat across from it. Apparently in the 1800's in Britain some wrenches were marked with the bolt size, not the head size.

[@gentlerowdy]

Than what’s SAE and AF relationship with ??

[@HartzHomestead]

That's all I know, and I found it by Googling it, because I had never heard of AF before. So try searching Google for more information.

[@TassieLorenzo]

@@gentlerowdy AF means across flats, the size across the flats of the bolt. Previously, British spanners were marked with the thread size so a wrench labelled 1/2" W (Whitworth) would fit a bolt with a 1/2" diameter and the bolt head size was defined as a mathematical function of the thread diameter (in this case .920" across the flats for a 1/2" W wrench). I.e., it was NOT 1/2" "across flats". Therefore the markings 1/2" W and 1/2" AF allowed you to tell the two different types of spanners apart. SAE and AF is the same.

[@brizzell2101]

Mad cool

[@angelafox4380]

Why is this so confusing to me?? Lol. Thank you for sharing.

[@HartzHomestead]

Well, they are 2 completely different systems, so one way to compare them is to translate both into thousandths of an inch. If numbers aren't fun for you, it's a lot to take in. I've always loved numbers, so for me it's like a mathematical puzzle.

[@zoozolplexOne]

Cool. !!!

[@world_still_spins]

Which companies make half sizes in metric? Like 20.5mm, 21.5mm, etc.

[@HartzHomestead]

I don't know. I've never heard of half metric size tools.

[@world_still_spins]

@@HartzHomestead Well hopefully some manufacturer turns it into something known. The amount of times I had as a mechanic and construction worker that neither SAE or Metric would fit a bolt/nut/fastener correctly, a half size Metric wrench/socket would have been helpful. (Yes there are obscure fractional SAE sizes such as 13/16" 27/32" 53/64", but remembering those can be a headache.)

[@HartzHomestead]

Actually, that's a brilliant idea, because metric is so logical, and that would cover most standard sizes that don't have an even metric equivalent. You could even get away with fewer standard wrenches.

[@6atlantis]

If I can only afford one set should I buy SAE or metric?

[@HartzHomestead]

I'd get metric if you'll mostly use it for vehicles, unless you have very old US vehicles. In the US for construction bolts or yard tools you might need SAE. If you get a metric set plus 1/4", 3/8", 1/2", and 11/16" that would cover most situations, also possibly 13/16", 1" and 1-1/8".

[@6atlantis]

@@HartzHomestead thanks

[@ninjagamer4515]

What is size larger than 9/32

[@HartzHomestead]

The next size bigger than 9/32" would be 5/16" or 8mm, which are almost identical.

[@n.c.2537]

Can I use a 15/16 instead of a 24mm?

[@HartzHomestead]

Yes, the 15/16" is .007 smaller than a 24mm, but that's close enough. It may fit tighter, which is actually good.

[@n.c.2537]

@@HartzHomestead it's just that I need to change the transfer case fluid on my Toyota Highlander and it has a 24mm drain plug and none of my local hardware stores have it and I could only find a 15/16 socket. But now with your help I'm about to tackle that job. Thanks!!!

[@varn4591]

11/16 female impact driver not exist 😅,nissan yu41 used that sizes

[@garrickwelsh6793]

What size nut goes on a 14mm bolt

[@HartzHomestead]

I don't know.

[@TassieLorenzo]

Depending on which standard it's following: ANSI ISO (American) will be a 21mm, DIN (German Standard) will be a 22mm and JIS (Japanese Industrial Standard) will be a 19mm. Newer BMWs use the ANSI ISO standard, however Mercedes still uses the DIN standard.

[@My2kClipz]

So 1/2 is a 13mm correct?

[@HartzHomestead]

Actually 1/2" is smaller. 13mm is 12 thousandths of an inch bigger, which is quite a bit. So if the bolt or nut is a 1/2", the 13mm will fit pretty loose. That might work OK if it's not very tight, but you could strip it if you have to apply a lot of force. If you can get a 1/2" on it, that will fit tighter and be better for the bolt or nut.

[@My2kClipz]

@@HartzHomestead I was removing my car batter the washer holding the screw needed a 13mm a 1/2 wrench got it off I will put it back on tomorrow and let you know how it go thanks a lot tho this video taught me something

[@BLK.214]

Chart Inch sa mm

[@NurulIslam-dy9jw]

SAE fullmeaning??

[@HartzHomestead]

It stands for Society of Automotive Engineers, which established measurements in feet and inches over 100 years ago. It also stands for Standard American English, a measuring system that includes gallons, pounds and ounces for volume and weight.

[@tonymoran9794]

Thanks!

[@brianj1203]

I’m trying to take off the upper control arm ball joint and it says I need an 18mm wrench 🔧 and I don’t have it. I can’t fit a socket on it because the axle is in the way..can I use a 3/4 wrench according to the chart or 11/16??

[@HartzHomestead]

There's not a good substitute for the 18mm. 3/4" will be too big and likely strip the bolt head. An adjustable wrench might work, if you have a good one you can get on there tight enough. If you can get an 11/16" on it, that would work, but it's 0.021" too small, so in a pinch you could file it down enough to make it fit, but you'd be better off to buy or borrow an 18mm.

[@TassieLorenzo]

@@HartzHomestead "There's not a good substitute for the 18mm" 18mm is close to 23/32", 23/32"=18.26mm

[@Fetguf]

Guess which country that converted to metric in 1866?

[@HartzHomestead]

The US didn't exactly convert to metric then, it just made it legal to use it. Apparently it didn't really catch on though - too bad.

[@user-it6gd6uh7e]

how to get chart

[@HartzHomestead]

You can download a chart using the links in the description below the video. The JPG chart is likely best for viewing on a phone, the others might depend of if your device can read a PDF or Word document. For a printed copy you'd also need access to a printer. Firefox blocked the Word document here, probably because I created it in 2007 Office, which is out of date. The advantage of Word is if you want to reformat or alter the chart you could make changes to it.