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Standard Screw Threads and Tap Drill Sizes
American Threads
No. | Thread | Tap Drill | Clear Drill |
---|---|---|---|
0 | 80 | 56 | 52 |
1 | 72 | 53 | 48 |
2 | 56 | 49 | 43 |
3 | 48 | 47 | 39 |
4 | 40 | 44 | 32 |
5 | 40 | 39 | 30 |
6 | 32 | 36 | 28 |
8 | 36 | 29 | 19 |
10 | 32 | 21 | 11 |
12 | 24 | 16 | 2 |
Size | Thread | Tap Drill |
---|---|---|
1/4 | 28 | 3 |
5/16 | 24 | I |
3/8 | 24 | Q |
7/16 | 20 | 25/64 |
1/2 | 20 | 29/64 |
Size | Thread | Tap Drill |
---|---|---|
1/4 | 20 | 7 |
5/16 | 18 | F |
3/8 | 16 | 5/16 |
7/16 | 14 | U |
1/2 | 13 | 27/64 |
9/16 | 12 | 31/64 |
5/8 | 11 | 17/32 |
British Threads
Size | Thread | Tap Drill |
---|---|---|
5/32 | 40 | #30 |
3/16 | 40 | 5/32 |
7/32 | 40 | 3/16 |
1/4 | 40 | 7/32 |
5/16 | 32 | J |
3/8 | 32 | Q |
3/8 | 40 | 11/32 |
Size | Diameter mm | Diameter inch | Tap Drill | Clear Drill |
---|---|---|---|---|
0 | 6.0 | 0.2362 | 10 | C |
1 | 5.3 | 0.2087 | 17 | 2 |
2 | 4.7 | 0.1851 | 24 | 12 |
3 | 4.1 | 0.1614 | 29 | 19 |
4 | 3.6 | 0.1417 | 32 | 27 |
5 | 3.2 | 0.1260 | 37 | 30 |
6 | 2.8 | 0.1102 | 43 | 34 |
7 | 2.5 | 0.0984 | 46 | 38 |
8 | 2.2 | 0.0866 | 50 | 43 |
9 | 1.9 | 0.0748 | 53 | 47 |
10 | 1.7 | 0.0670 | 55 | 50 |
11 | 1.5 | 0.0591 | 56 | 52 |
12 | 1.3 | 0.0512 | 60 | 54 |
14 | 1.0 | 0.0394 | 70 | 59 |
Machine Screw Diameters
The Miniature Locomotive, July-August 1954
Machine screws are numbered as distinct from Cap Screws, Bolts, etc, and range usually from #0 to #12. A convenient method of finding the exact diameter if a table is not handy is as follows:
- Multiply the number of 13 and add sixty thousandths. The answer will be thousandths.
Examples:
- #0 -- 0 multiplied by 13 equals 0, plus 0.060 equals 0.060
- #3 -- 3 multiplied by 13 equals 39, plus 0.060 equals 0.099
- #5 -- 5 multiplied by 13 equals 65, plus 0.060 equals 0.125
- #10 -- 10 multiplied by 13 equals 0.130, plus 0.060 equals 0.190
Model Pipe Threads
NPT American National Standard Tapered Pipe Thread
NPT is a North American tapered pipe standard.
MTP Model Taper Pipe
MTP is a North American tapered pipe standard designed specifically for small live steam models.
METP Model Engineer Taper Pipe
METP is the British equivalent of the North American MTP.
ME Model Engineering (British Straight Thread)
ME is a British, non-tapered (straight) thread.
UNS American National Standard Unified Special
UNS is a non-tapered (straight) thread.
From Wikipedia:
- The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries. It has the same 60° profile as the ISO metric screw thread, but the characteristic dimensions of each UTS thread (outer diameter and pitch) were chosen as an inch fraction rather than a millimeter value. The UTS is currently controlled by ASME/ANSI in the United States.
UST Universal Straight and Taper
UST is a proprietry tapered thread designed by PM Research.
Comments
Ciszewski posted on PracticalMachinist.com:
- You can tap NPT without taper reaming. Morse Cutting Tools recommends:
- 1/4 NPT - drill with a 7/16 bit to a minimum depth of 0.78125 & tap to a depth of 0.72525
- 3/8 NPT - drill with a 37/64 bit to a minimum depth of 0.8125 & tap to a depth of 0.7565
- 1/2 NPT - drill with a 45/64 bit to a minimum depth of 1.03125 & tap to a depth of 0.96025
- Following these recommendations will only give you a full thread for the first 2 to 3 threads.