How do I figure out the size of this nut?

[cnczoner]

Seriously, as simple as it sounds, I just need to find a nut to put on the end of a ballscrew, and I don't have a metric thread gauge, so I figured I'd measure. Pitch is definitely 1.5mm, and measuring the major diameter with a caliper gives me 20.2mm. So is it M21 x 1.5? or M22? Or...??? Is there some standard (percentage) for which the major diameters are cut down to, relative to the specified size?

This wikipedia page lists M20 and M22 as having 1.5mm pitches -- is this across the board? Or is it possible that someone makes larger nuts with 1.5mm pitch? I doubt that list is complete because I've seen M21 nuts.

I don't want to have to order different sizes (especially since I'll probably have to buy a pack of 10 or more), just to get one single nut.

Anyone know for sure how to figure this out?

Cheers,
-Neil.

[Mitsui Seiki]

20.2mm?
It has to be M20x1.5.
M22 has a major Dia. of 22mm and M21 doesn't excist.

You can get a nut up M80 with 1.5 pitch.

[Konrad]

Could it be a 13/16" OD, 1/16 pitch?

Konrad

[cnczoner]

I thought that if I measured 20.2mm it would've been bigger. I dug through the yellow pages and found a local supplier who carried metric nuts and it turned out to be an M20 x 1.5. I figured it would've been more clear-cut to figure out the nut size based on a couple measurements.

Thanks,
-Neil.