Small screw thread standard
Small screw thread standard
(OP)
Folks-
You know how a #4(.112)-40 UNC-2B machine screw thread callout defines the nominal size (.112), pitch (40 thds/inch), series (Unified National Coarse), tolerance class (2), and gender (B=internal)?
What about 00, 000, and 0000 threads? How would one call out, say, a 0000 internal machine screw thread in a part? I've been having a devil of a time determining what to use for the series, tolerance class, and gender. Also, what (if any) is the governing standard for these oddballs?
You know how a #4(.112)-40 UNC-2B machine screw thread callout defines the nominal size (.112), pitch (40 thds/inch), series (Unified National Coarse), tolerance class (2), and gender (B=internal)?
What about 00, 000, and 0000 threads? How would one call out, say, a 0000 internal machine screw thread in a part? I've been having a devil of a time determining what to use for the series, tolerance class, and gender. Also, what (if any) is the governing standard for these oddballs?
Tunalover





RE: Small screw thread standard
I use 4-40 threads all the time. My callout for a tapped hole is...
4-40UNC-2B
Some people prefer .112-40UNC-2B, but I am not certain this is written on the tap or the thread gauge the worker has to select. The B is internal. See the Machinery's Handbook.
The above specification completely defines the thread as per the Unified National specification.
JHG
RE: Small screw thread standard
You're preaching to the choir. How about my question?
Tunalover
RE: Small screw thread standard
CODE
Gauge Decimal TPI TPI Size Millimeter
No.0000 0.021 160 - - 0.53
No.000 0.043 120 - 3/32" 0.86
No.00 0.047 90 - 3/32 1.19
No.0 0.060 - 80 5/32" 1.524
No.1 0.073 64 72 5/32" 1.854
No.2 0.086 56 64 3/16" 2.184
No.3 0.099 48 56 3/16" 2.515
No.4 0.112 40 48 1/4" 2.845
No.5 0.125 40 44 1/4" 3.175
No.6 0.138 32 40 5/16" 3.505
No.8 0.164 32 36 11/32" 4.166
No.10 0.190 24 32 3/8" 4.826
No.12 0.216 24 28 7/16" 5.486
1/4" 0.250 20 28 7/16" 6.349
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www.tailofthedragon.com
RE: Small screw thread standard
Oops! Sorry.
There is a standard in the Machinery's Handbook for Unified Minature Screw Threads, but it is metric. The intruction paragraph states that existing minature screw threads are "improvised and unsystematized".
If your standard is not official, would it be acceptable to call up the tap and inspection gauge by manufacture and part number?
JHG
RE: Small screw thread standard
htt
RE: Small screw thread standard
What's your source?
Kenneth-
Machinery's Handbook talks about UNM threads and they are different from 00, 000, and 0000 screw threads. In fact I have the ASME standard for the UNM and they don't mention those sizes.
Drawoh-
I suppose it would be OK to do it that way but it effectively sole-sources the tooling to one mfgr. For high-volume production that's not a good thing. That's the good thing about standardization!
Tunalover
RE: Small screw thread standard
ht
RE: Small screw thread standard
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RE: Small screw thread standard
What in the world is "zytrax"? Just wondering...
Tunalover