How to fix 10mm socket, 6mm bolt threads at home with a bolt tap

6mm bolt threads on this honda engine head were stripped by previous owners. Get a 1/4-20 tap and 1/4-20 bolts accordingly to substitute the 6mm thread ones. Directly tap into the damaged 6mm thread gently and with lubricant oil, clean and measure. DO IT AT YOUR OWN RISK. If you want to create a new hole somewhere else for this specific Tap, the drill bit size is #7
This fix is possible when the next thread size is very close to the original one, normally this would mean you will need to change from a metrical bolt to a standard one like it is shown here or vice versa. However in some cases the next thread size available is too big and will need drilling before tapping. If you don't have enough space available for a bigger thread, then it will be time to consult a Machine Shop for the best fix available and Get Your Wallet Ready To Drop A Few 20's Over Their Counter Afterwards.