spark plug thread size

[jiggersplat]

i need to do a compression test and my gauge is the wrong size.  can anyone tell me offhand what size thread adapter/gauge i need?  stupid bike is only firing on one cylinder again.  it has fuel and seems to have spark, so that pretty much leaves compression.

thanks,
dan

[MarkusN]

I'ts 12 mm. Dunno about pitch, but I assume for spark plug's there is only one 12 mm standard.