Pan cover screws

ratchet449mc
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Re: Pan cover screws

#31

Post by ratchet449mc »

Well maybe this horse is finally dead...lol... I found that 3/16-24 is categorized as NS... National Special..... :roll:
awander
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Re: Pan cover screws

#32

Post by awander »

For those who have not yet fallen asleep from boredom:

I found a bit more info on the 3/16-24 thread.

Greenfield Tap & Die offered the thread in their 1916 Catalog #37. They were listed as US form.

I also found pictures on the Internet of Greenfield Little Giant Die sets, where some sets listed the thread as USS(U.S. Standard, also known as Sellers Profile, and Franklin Institute Thread), and some listed it as NS(National Special).

The USS threads were adopted as a standard in around 1864.

The National threads were adopted around 1921, and superseded the USS, SAE,and ALAM threads which were used at that time.

USS and National thread forms used a thread with a flat at both the crest and the root of the thread, equal in width to 1/8 of the pitch. So for a 24TPI thread, the pitch is 1/24 or 0.0417, and 1/8 of that is 0.0052, or just over five thousandths of an inch wide for the flat.

Unified Threads were adopted in 1949, and superseded the National threads.

The Unified thread forms differed from USS/National in that the flat at the crest of an external thread(and the flat at the root of an internal thread) stayed equal in width to 1/8 of the pitch; while the flat at the root of an external thread(and the flat at the crest of an internal thread) was made equal in width to 1/4 of the pitch.
awander
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Re: Pan cover screws

#33

Post by awander »

ratchet449mc wrote:Well maybe this horse is finally dead...lol... I found that 3/16-24 is categorized as NS... National Special..... :roll:
Yeah, I found that Greenfield Tap & Die called it that(3/16-24NS) on some of their tap & die sets, but I haven't found 3/16 listed in any of the actual standards documents. The latest doc I found relating to the National thread series is the 1933 "Report of the National Screw Thread Commission" to the National Bureau of Standards, and all sizes smaller than 1/4" are listed as number sizes, not fractional.
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Re: Pan cover screws

#34

Post by Larry »

The 3/16-24 thread must be specified somewhere in Harley documentation; I just don't know where to look.
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