BOLT SIZES

[Tim Farr]

I'm looking at the Screwfix catalogue. The diameter of bolts and threaded rod is listed as M3, M4, M5, M6 and so on; does this mean 3mm, 4mm etc.

 

[^woody^]

yes and M if for metric so as not to confuse the old fogeys with their whitworths and whatnots

 

[Tim Farr]

Thanks Woody

 

[Hitachimad]

The number is pretty much the mean diameter bar the thread is cut from.
So for example, an M10 bolt would be a close fit in a 10mm diameter hole.