Thread Standard Question
Thread Standard Question
(OP)
Hi All,
I'm selecting a thread standard for a nominal 1-9/16" diameter engagement, but am confused by what I see in Machinery's Handbook. The internal threads/inch of 6, 8, 12 and 16 are all listed as UN, then 18 is listed as UNEF and then 20 is listed back at UN. Can anyone explain why the 20 threads per inch would not even be considered fine-pitch while the 18 is listed as extra-fine?
I like the slightly greater clearance the minor diameter of the 20 will provide for a solid piece that has to fit thru before the externally-threaded feature comes in, but I am aware of the pros/cons associated with coarse/fine/extra-fine, so I want to make sure I understand the basis for this designation. Some of the other nominal diameters have this, too - 1-1/2", 5/16" to name a couple.
- Eric
I'm selecting a thread standard for a nominal 1-9/16" diameter engagement, but am confused by what I see in Machinery's Handbook. The internal threads/inch of 6, 8, 12 and 16 are all listed as UN, then 18 is listed as UNEF and then 20 is listed back at UN. Can anyone explain why the 20 threads per inch would not even be considered fine-pitch while the 18 is listed as extra-fine?
I like the slightly greater clearance the minor diameter of the 20 will provide for a solid piece that has to fit thru before the externally-threaded feature comes in, but I am aware of the pros/cons associated with coarse/fine/extra-fine, so I want to make sure I understand the basis for this designation. Some of the other nominal diameters have this, too - 1-1/2", 5/16" to name a couple.
- Eric





RE: Thread Standard Question
RE: Thread Standard Question
The other UN sizes are not commonly available, i.e. you will need to have mating hardware specially made to that pitch; but the standard covers all of the tolerances.
(*)This is MY definition of a well-stocked hardware store, YMMV on finding EF threaded fasteners in any hardware store near you...
RE: Thread Standard Question
RE: Thread Standard Question
The linked chart shows how arbitrary the conversion was.
http://www.amesweb.info/Screws/Tables/Thread-Pitch...