M30 diameter
 

Morning,

Not car related...

So I know an m30 bolt is 30mm diameter to the outer edge of the threads....but does 29.6mm qualify as an m30?

I'm changing the trv heads on my rads.

The M30 designation is only the nominal diameter, there will always be a tolerance, 29.6 is near enough, do not worry, the top of the thread is always slightly rounded to ensure clearance when fitted..

Are metric threads used on plumbing parts? I always thought they were BSP, but maybe it's changed?


TC

29.6mm (How/with what are you measuring it?) is closer to 30mm than either 3/4" BSP or 1"BSP

Just looked up Metric thread tolerancing and depending on the grade the minimum O/D could be 29,522mm, max O/D 29.947mm, so 29.6mm could well be a nominal 30mm

If you're changing the TRV's and wondering what size thread they are then as far as I know they're std, so you can't go wrong.

I think you may be correct, BSP is still used on iron and brass pipe fittings as I've used them recently when changing gas meters.

Get a set of Zeus charts and you can check the pitch just to be sure, they've proved very useful for when I've been checking screws and bolts.

Zues been over 30 years since I last heard that when I was an apprentice

They certainly are on trv heads

With a cheapy Chinese digital caliper

Good enough for me!

As far as I can tell there are at least 3 different sizes depending on age and manufacturer!