USCTI Table 311 specifies dimensions for standard pipe taps with straight and taper ground threads, covering nominal sizes from 1/16 inch to 4 inches. The table provides overall length, thread length, square length, shank diameter, size of square, and optional neck dimensions with corresponding tolerances. These dimensions apply to both straight and taper pipe taps used for threading pipe connections.
General dimensions for pipe taps
The table below lists the standard dimensions in inches for pipe taps from 1/16 inch to 4 inch nominal size.
| Nominal Size (Inches) | Overall Length L | Thread Length l | Square Length l2 | Shank Diameter d1 | Size of Square a | Length Optional Neck |
|---|---|---|---|---|---|---|
| 1/16 | 2.13 | .69 | .38 | .3125 | .234 | .375 |
| 1/8 | 2.13 | .75 | .38 | .3125 | .234 | …. |
| 1/8 | 2.13 | .75 | .38 | .4375 | .328 | .375 |
| 1/4 | 2.44 | 1.06 | .44 | .5625 | .421 | .375 |
| 3/8 | 2.56 | 1.06 | .50 | .7000 | .531 | .375 |
| 1/2 | 3.13 | 1.38 | .63 | .6875 | .515 | …. |
| 3/4 | 3.25 | 1.38 | .69 | .9063 | .679 | …. |
| 1″ | 3.75 | 1.75 | .81 | 1.1250 | .843 | …. |
| 1-1/4 | 4.00 | 1.75 | .94 | 1.3125 | .984 | …. |
| 1-1/2 | 4.25 | 1.75 | 1.00 | 1.5000 | 1.125 | …. |
| 2″ | 4.25 | 1.75 | 1.13 | 1.8750 | 1.406 | …. |
| 2-1/2 | 5.50 | 2.56 | 1.25 | 2.2500 | 1.687 | …. |
| 3″ | 6.00 | 2.63 | 1.38 | 2.6250 | 1.968 | …. |
| 3-1/2 | 6.50 | 2.69 | 1.50 | 2.8125 | 2.108 | …. |
| 4″ | 6.75 | 2.75 | 1.56 | 3.0000 | 2.250 | …. |
What are the tolerances for pipe tap dimensions?
Tolerances vary by element and size range, with most dimensions having minus-only tolerances to ensure proper fit. The table below specifies all tolerances for pipe tap dimensions.
| Element | Size Range | Direction | Tolerance |
|---|---|---|---|
| Overall Length – L | 1/16 to 3/4 inc. | Plus or Minus | .031 |
| Overall Length – L | 1″ to 4″ inc. | Plus or Minus | .063 |
| Thread Length – l | 1/16 to 3/4 inc. | Plus or Minus | .063 |
| Thread Length – l | 1″ to 1-1/4″ inc. | Plus or Minus | .094 |
| Thread Length – l | 1-1/2 to 4″ | Plus or Minus | .125 |
| Square Length – l2 | 1/16 to 3/4 inc. | Plus or Minus | .031 |
| Square Length – l2 | 1″ to 4″ inc. | Minus | .063 |
| Shank Diameter – d1 | 1/16 to 1/8 inc. | Minus | .0015 |
| Shank Diameter – d1 | 1/4″ to 1″ inc. | Minus | .0020 |
| Shank Diameter – d1 | 1-1/4″ to 4″ inc. | Minus | .0030 |
| Size of Square – a | 1/16 to 1/8 inc. | Minus | .004 |
| Size of Square – a | 1/4 to 3/4 inc. | Minus | .006 |
| Size of Square – a | 1″ to 4″ inc. | Minus | .008 |
Where can I find thread limits and eccentricity tolerances?
For thread limits and tolerances, see Tables 335, 335A and 338. For eccentricity tolerances of taps, see Table 317.
Source and updates
Source: taylortool.com engineering data. Reviewed September 2026.