This is a new numbering system I am hearing for the first time. Like A&N hose fittings, even re-bar as a #3 is 3/8”, #4 is 1/2” and so on. But, the world has shrunk somewhat since air cleaners had 1 qt of motor oil to protect from dirt, dust, June bugs and butterflies. Our large family farm was only 25 miles from the Capitol city, but the rural areas were last to be updated so we had a telephone the was a party line and crank on the side of rectangular wall mounted box to get the operator. Surprise, my grandmother was the operator. The beautiful oak board-desk combo and with a head set would ask to whom you wish to be connected, Eddy at the Mobile Gas Station, they pull out a weighted cord with weight, roller on wire wrapped in cotton and 1/4” plugs marked with names as the town 3.5 miles away had 120 people maybe. As close as “Mayberry” and Sarah the phone operator as you could get. Your drivers license had no photo and at age 13, it said “Farm / School” so good to go on gasoline at $0.199 cent per gallon. Yes, 19 cents plus 9th of a penny tacked on for profit! The is a nice river gun as I just hit my 50th year of buying SnapOn tools and all the pneumatic tools were Chicago Pneumatic not SnapOn and a paint gun, a Binks #7 siphon feed cost $29.00. Still have it and the receipt!