Thread Confusion

[stuartpaul]

This may well be a silly question but please bear with me on this as I just don't know the answer!

I was just about to press the 'buy now' button for some M4 thread inserts (see separate thread) for door knobs when I suddenly wondered what the diameter of my knob screws (really?! ) was.

They measure at 3.7 mm so I was left wondering if they're to small for M4?

I also measured some other screws for fixing knobs (better? :shock: ) and they were also 3.7 mm.

They'd probably also be too big for M3.5 so I'm left wondering what to do next.

Any help gratefully appreciated.

 

[pcb1962]

An M4 bolt starts off at 4mm dia, so by the time the little triangle at the top has been removed 3.7mm sounds about right

 

[AndyT]

Also, if you look deeper into the topic of threads and standards, there are different grades of fit. A simple item like a door knob would be made to a smaller size/sloppier fit than a piece of precision laboratory gear or something in a jet engine.

 

[SteveF]

if it helps
i recently needed to fit some nuts to standard knobs...they was m4

Steve

 

[stuartpaul]

Thank you all - M4 it is