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Small screw thread standard

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?

Tunalover

RE: Small screw thread standard

Tunalover,

   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

(OP)
drawoh-
You're preaching to the choir.  How about my question?

Tunalover

RE: Small screw thread standard

CODE

          Inches   UNC     UNF     NUT       
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
Heres to ya Tuna!

_______________________________________
Feeling frisky.........
www.tailofthedragon.com

RE: Small screw thread standard

Tunalover,

   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

(OP)
Pressed-
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

zytrax

_______________________________________
Feeling frisky.........
www.tailofthedragon.com

RE: Small screw thread standard

(OP)
Pressed-
What in the world is "zytrax"?  Just wondering...

Tunalover

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