Thread sizes

[stryd_one]

Hey dudes...

I've found a part that I'd like to get, it's a silicone boot with a built-in mounting nut for waterproofing a pushbutton. The thread size is specified as 3/8-27NS-2B . I know that's a 3/8" diameter, but the rest is freakin Martian speak to me.

I hope someone can shed some light on this for me, cause I'm now trying to find suitably threaded switches, and many of them have a far shorter description of the thread, like just 3/8" or 3/8-31 or something, and I'm not sure whether they will fit...

Even better would be a suitable bushing, like a threaded metal tube with a lip. I'd also appreciate it if anyone could help me find a source for those. I've attached a pic to show what I mean... The idea being that I can then panel mount the seal by screwing it onto the bushing, and PCB mount the switch and pass the button through the bushing.

Thanks for any advice you have :)

bushing.JPG

[smashtv]

3/8-27NS-2B . I know that's a 3/8" diameter, but the rest is freakin Martian speak to me.

No doubt on the martian speak!

Let's break it down: 3/8"-27NS-2B=

'3/8"'=diameter

'27'=TPI (Threads per inch)

'NS'=American National Thread-Special.  A WW2 era notation for the shape of the threads.  In practice equivalent to 'UNS' (Unified Thread-Special)  A quote from my tap book:

"The UNS series is a catch-all category for threads which have the American Standard form, but whose pitches are not in the Unified Coarse (UNC) or Unified Fine (UNF) series."

The easy way to remember this code is to think Non-Standard.  ;D

'2B'=This is a code for the tolerance class, A for screws and B for nuts.  There are three classes, think of this as the slop factor. 

'1B' is pretty slack, think Chinese pot-metal screws in a knock-off widget. 

'2B' is tigher, but allows for finish/plating, etc. 

'3B' is tight. 

In modern manufacturing, 1B is part of a machinist' punchline when joking, 3B is for locknuts, buzzword marketing and 'beat it to fit, paint it to match' engineering, and 2B fit is king.  ;)

Of course all of this goes out the window for metric stuff.  Metric uses 'xH' for tolerance classes, has different standard thread designations, etc....

For this type of hardware (switch nuts, encoder nuts, etc.) they use non standard threading to get the best grip with the least thread length, hence the odd pitches/thread profiles.  That puts us in roll-the-dice land when matching hardware between manufacturers.  :-\

Best

Smash

[stryd_one]

That puts us in roll-the-dice land when matching hardware between manufacturers.  :-\

Hah you got that right! I can't find any switches or bushings to match these things, at all, whatsoever. Damn!

Edit: I really do wonder why a company like APM would make boots for a nonexistent switch... Perhaps this is just a legacy part?

Thanks for the info though man :)