Unified National Coarse dimensions in inch and millimetre, covering #0 through 1-1/2".
Unified National Coarse is the inch-series default, and it still turns up on imported machinery, hydraulic fittings and legacy spares. Dimensions are given in both inch and millimetre because Indian maintenance drawings are routinely marked up in whichever unit the original equipment used.
Basic dimensions to ASME B1.1, adopted in India as IS 4406. Thread angle 60°.
| Size | TPI | Pitchmm | Major Øin | Pitch Øin | Pitch Ømm | Minor Ø ext.in | Minor Ø int.in |
|---|---|---|---|---|---|---|---|
| #0-80 | 80 | 0.318 | 0.06 | 0.0519 | 1.318 | 0.0447 | 0.0465 |
| #1-64 | 64 | 0.397 | 0.073 | 0.0629 | 1.598 | 0.0538 | 0.0561 |
| #2-56 | 56 | 0.454 | 0.086 | 0.0744 | 1.89 | 0.0641 | 0.0667 |
| #3-48 | 48 | 0.529 | 0.099 | 0.0855 | 2.172 | 0.0734 | 0.0764 |
| #4-40 | 40 | 0.635 | 0.112 | 0.0958 | 2.433 | 0.0813 | 0.0849 |
| #5-40 | 40 | 0.635 | 0.125 | 0.1088 | 2.764 | 0.0943 | 0.0979 |
| #6-32 | 32 | 0.794 | 0.138 | 0.1177 | 2.99 | 0.0997 | 0.1042 |
| #8-32 | 32 | 0.794 | 0.164 | 0.1437 | 3.65 | 0.1257 | 0.1302 |
| #10-24 | 24 | 1.058 | 0.19 | 0.1629 | 4.138 | 0.1389 | 0.1449 |
| #12-24 | 24 | 1.058 | 0.216 | 0.1889 | 4.798 | 0.1649 | 0.1709 |
| 1/4"-20 | 20 | 1.27 | 0.25 | 0.2175 | 5.525 | 0.1887 | 0.1959 |
| 5/16"-18 | 18 | 1.411 | 0.3125 | 0.2764 | 7.021 | 0.2443 | 0.2524 |
| 3/8"-16 | 16 | 1.588 | 0.375 | 0.3344 | 8.494 | 0.2983 | 0.3073 |
| 7/16"-14 | 14 | 1.814 | 0.4375 | 0.3911 | 9.934 | 0.3499 | 0.3602 |
| 1/2"-13 | 13 | 1.954 | 0.5 | 0.45 | 11.43 | 0.4056 | 0.4167 |
| 9/16"-12 | 12 | 2.117 | 0.5625 | 0.5084 | 12.913 | 0.4603 | 0.4723 |
| 5/8"-11 | 11 | 2.309 | 0.625 | 0.566 | 14.376 | 0.5135 | 0.5266 |
| 3/4"-10 | 10 | 2.54 | 0.75 | 0.685 | 17.399 | 0.6273 | 0.6417 |
| 7/8"-9 | 9 | 2.822 | 0.875 | 0.8028 | 20.391 | 0.7387 | 0.7547 |
| 1"-8 | 8 | 3.175 | 1 | 0.9188 | 23.338 | 0.8466 | 0.8647 |
| 1-1/8"-7 | 7 | 3.629 | 1.125 | 1.0322 | 26.218 | 0.9497 | 0.9704 |
| 1-1/4"-7 | 7 | 3.629 | 1.25 | 1.1572 | 29.393 | 1.0747 | 1.0954 |
| 1-3/8"-6 | 6 | 4.233 | 1.375 | 1.2667 | 32.174 | 1.1705 | 1.1946 |
| 1-1/2"-6 | 6 | 4.233 | 1.5 | 1.3917 | 35.349 | 1.2955 | 1.3196 |
Internal threads are checked with a thread plug gauge — a matched GO / NO-GO pair — and external threads with a thread ring gauge or a calibrated snap gauge. Setting plugs keep the rings in calibration between recertifications.
DSN manufactures UNC plug gauges, ring gauges and setting plugs at the Coimbatore works, cut and lapped as matched pairs and issued with traceable calibration certificates. Send a drawing or a thread designation and we will quote to it.