Posted by DC31k on 21/08/2023 17:21:17:
Posted by Mick B1 on 21/08/2023 13:55:49:
I can screw an M20 x 1.5 thread several turns into the tray drain on my WM250V. If it was anything different I don't think I could do that.
If it is clearly a drain point, meant for coolant, the most likely thread is that used in conjunction with pipework, i.e. BSP.
M20 x 1.5 is a standard thread on electrical conduit, which generally is not used to carry liquids. That thread would be found on an electric motor, for a cable gland in the same way that a BSP thread would not be found on a motor.
M20 x 1.75 is extremely unlikly as 1.75mm pitch is not used anywhere in metric threads other than standard M12 coarse.
What I am saying is that the purpose of the thread can be a good pointer to its specification.
I don't disagree, and I know of the conduit application, but I can screw the M20 x 1,5 thread in 6 turns before it sticks, and the drain's position and its welded-on strainer make it practically impossible to tell whether the thread runs out or gets jammed with paint or crud at that point.
The only standard BSP thread that's *anywhere near* the same OD is 1/2", nearly 38 thou bigger and 14 TPI or ~1,8143 mm pitch. Can't see an M20 x 1,5 male thread fitting that even for 1 turn.
I've seen some evidence of variation in some parts used in lathes believed to be from the same factory. I don't know whether these are properly-documented Engineering Changes in these factories, or casual pragmatism to use up whatever they happen to have at the time.