question on making sense of thread sizes

I have a stripped out fork cover bolt on a 08 yz250f and i found on rocky mountain a tusk thread repair kit and they have a couple sizes to choose from and I'm not sure what it is.

The choices are:

M5) 5mm x .8mm thread pitch

M6) 6mm x 1.0mm thread pitch

M8) 8mm x 1.25 thread pitch

Its a 8mm bolt but im not sure the thread pitch since i dont have a thread gauge which i was assuming was the length in between the threads, but not sure!

So does anyone know what size i would need in the kit or explain what the different sizes in the choices represent.? the kit gives you a drill bit to drill damaged threads out and a tap to make new ones to thread in a heli coil for the original bolt.

-Any help appreciated

Thanks!

Sorry after rereading after i posted this i thought id clarify its the hole on the fork thats striped, not the bolt itself, but probably could've figured that!!

thanks

I have a '05 YZ125 and I think it's the same bolt... If no one helps you out I'll get the thread gauge on it soon.

Motorcycle fasteners do not follow ISO standards for head sizes and thread sizes but they are fairly standard. You will not find a 5mm bolt anywhere outside of the engine on your bike. A bolt with an 8mm head (fits an 8mm wrench) will most likely be a 6mm x 1.00 thread. 10mm head bolts can be either 6 or 8 mm thread. 12mm head bolts will be a 8mm x 1.25 thread. If you have an 8 or a 12 mm head you know what size of bolt you have. If you have a 10 compare it to either an 8 or 12 mm head bolt and you will know if its the larger or smaller thread.

For ISO threads the size of the bolt describes the diameter of the threaded portion of the bolt. The pitch is the distance between threads.

Edited by 1987CR250R

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