[GreenKeys] ASR-33 mounting screws

[Randy and Sherry Guttery]

Someone wrote:
> The American National standard for machine screws has two thread pitches for 
> each screw size:  coarse and fine.  
If we're going to pick nits -- some screw sizes have three standard 
pitches - the third being extra fine (NEF) --
> The #6-40 IS a standard thread, it's 
> just the fine thread instead of the more commonly used #6-32 coarse thread.
>   
#6 screw being one size that indeed includes a third "recognized" pitch 
- at 6-48.  However - it's not considered a "standard" either - and is 
grouped with the catch-all class of NS (National Special).  Of course 
these days the "Official" policy is to discourage use of these less 
common pitches - but then they also "discourage" the use of #12 screws 
of any pitch - which is of course of consequence to us - as #12 is 
fairly common in older (military surplus, etc.) gear. I've had a couple 
of six-footer relay racks - in which all of the threaded holes on the 
equipment mounting rails were #12-32 screws - a double whammy in 
standards terms - as being both the "discouraged" #12 AND a NS (National 
Special) thread...

Since a lot of us have old military gear - it's a good idea to keep such 
in mind. Something I found extremely useful in dealing with mountains of 
screws (at one point we had two "hell boxes" one weighed well over five 
pounds while the larger one was approaching 20 pounds - we recently 
sorted both - took several days worth of spare time) - is a screw 
checker.  Here's the one we have:

<http://www.threadtoolsupply.com/sae-inch-screw-checker.html>

Unlike the cheap plastic ones - this thing is thick - and the holes are 
threaded allowing each screw gauge and pitch to be quickly identified. 
Note that it covers the most common sizes plus several NS sizes of 
interest to us with older gear. Having through holes for checking marred 
drill bits is nice - as is having the tap size drill listed for each 
gauge/pitch combination.

Just my .02...

-- 
randy guttery 

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