USCTI Table 303 specifies dimensions for special fine pitch taps with ground threads in the short series. Unless otherwise specified, these dimensions apply to taps from 1.010 to 1.510 inch diameter with 14 or more threads per inch (or 1.75 millimeter pitch and finer), and taps over 1.510 inch diameter with 10 or more threads per inch (or 2.5 millimeter pitch and finer). The table covers both fractional inch and metric tap sizes from 1-1/16 inch through 4 inches.
What pitch qualifies as fine pitch for special taps?
Fine pitch is defined differently depending on tap diameter. For taps 1.010 to 1.510 inch diameter inclusive, fine pitch means 14 or more threads per inch or 1.75 millimeter pitch and finer. For sizes over 1.510 inch diameter, fine pitch means 10 or more threads per inch or 2.5 millimeter pitch and finer.
Standard dimensions for special fine pitch taps, short series
The table below lists general dimensions for special thread taps in the short series with ground threads.
| Nominal Diameter Range (Inches) | Nominal Fractional Diameter (Inches) | Nominal Metric Diameter Millimeters (Inch) | Overall Length L | Thread Length l | Square Length l2 | Square Diameter d1 | Size of Square a |
|---|---|---|---|---|---|---|---|
| Over 1.010 To 1.073 (Inc.) | 1-1/16 (1.0625) | M27 (1.0630) | 4.00 | 1.50 | 0.88 | .8960 | 0.672 |
| Over 1.073 To 1.135 (Inc.) | 1-1/8 (1.1250) | 4.00 | 1.50 | 0.88 | .8960 | 0.672 | |
| Over 1.135 To 1.198 (Inc.) | 1-3/16 (1.1875) | M30 (1.18111) | 4.00 | 1.50 | 1.00 | 1.0210 | 0.766 |
| Over 1.198 To 1.260 (Inc.) | 1-1/4 (1.2500) | 4.00 | 1.50 | 1.00 | 1.0210 | 0.766 | |
| Over 1.260 To 1.323 (Inc.) | 1-5/16 (1.3125) | M33 (1.2992) | 4.00 | 1.50 | 1.00 | 1.1080 | 0.831 |
| Over 1.323 To 1.385 (Inc.) | 1-3/8 (1.3750) | 4.00 | 1.50 | 1.00 | 1.1080 | 0.831 | |
| Over 1.358 To 1.448 (Inc.) | 1-7/16 (1.4375) | M36 (1.4173) | 4.00 | 1.50 | 1.00 | 1.2330 | 0.925 |
| Over 1.448 To 1.510 (Inc.) | 1-1/2 (1.5000) | 4.00 | 1.50 | 1.00 | 1.2230 | 0.925 | |
| Over 1.510 To 1.635 (Inc.) | 1-5/8 (1.625) | M39 (1.5354) | 5.00 | 2.00 | 1.13 | 1.3050 | 0.979 |
| Over 1.635 To 1.760 (Inc.) | 1-3/4 (1.7500) | M42 (1.6535) | 5.00 | 2.00 | 1.25 | 1.4300 | 1.072 |
| Over 1.760 To 1.885 (Inc.) | 1-7/8 (1.8750) | 5.00 | 2.00 | 1.25 | 1.5190 | 1.139 | |
| Over 1.885 To 2.010 (Inc.) | 2 (2.0000) | M48 (1.8898) | 5.00 | 2.00 | 1.38 | 1.6440 | 1.233 |
| Over 2.010 To 2.135 (Inc.) | 2 1/8 (2.1250) | 5.25 | 2.00 | 1.38 | 1.7690 | 1.327 | |
| Over 2.135 To 2.260 (Inc.) | 2 1/4 (2.2500) | M56 (2.2047) | 5.25 | 2.00 | 1.44 | 1.8940 | 1.420 |
| Over 2.260 To 2.385 (Inc.) | 2 3/8 (2.3750) | 5.25 | 2.00 | 1.44 | 2.0190 | 1.514 | |
| Over 2.385 To 2.510 (Inc.) | 2 1/2 (2.5000) | 5.25 | 2.00 | 1.50 | 2.1000 | 1.575 | |
| Over 2.510 To 2.635 (Inc.) | 2 5/8 (2.6250) | M64 (2.5197) | 5.50 | 2.00 | 1.50 | 2.1000 | 1.575 |
| Over 2.635 To 2.760 (Inc.) | 2 3/4 (2.7500) | 5.50 | 2.00 | 1.50 | 2.1000 | 1.575 | |
| Over 2.760 To 2.885 (Inc.) | 2 7/8 (2.8750) | M72 (2.8346) | 5.50 | 2.00 | 1.50 | 2.1000 | 1.575 |
| Over 2.885 To 3.010 (Inc.) | 3 (3.0000) | 5.50 | 2.00 | 1.50 | 2.1000 | 1.575 | |
| Over 3.010 To 3.135 (Inc.) | 3 1/8 (3.1250) | 5.75 | 2.00 | 1.50 | 2.1000 | 1.575 | |
| Over 3.135 To 3.260 (Inc.) | 3 1/4 (3.2500) | M80 (3.1496) | 5.75 | 2.00 | 1.50 | 2.1000 | 1.575 |
| Over 3.260 To 3.385 (Inc.) | 3 3/8 (3.3750) | 5.75 | 2.00 | 1.50 | 2.1000 | 1.575 | |
| Over 3.385 To 3.510 (Inc.) | 3 1/2 (3.5000) | 5.75 | 2.00 | 1.50 | 2.1000 | 1.575 | |
| Over 3.510 To 3.635 (Inc.) | 3 5/8 (3.6250) | M90 (3.5433) | 6.00 | 2.00 | 1.75 | 2.1000 | 1.575 |
| Over 3.635 To 3.760 (Inc.) | 3 3/4 (3.7500) | 6.00 | 2.00 | 1.75 | 2.1000 | 1.575 | |
| Over 3.760 To 3.885 (Inc.) | 3 7/8 (3.8750) | 6.00 | 2.00 | 1.75 | 2.1000 | 1.575 | |
| Over 3.885 To 4.010 (Inc.) | 4 (4.0000) | M100 (3.9370) | 6.00 | 2.00 | 1.75 | 2.1000 | 1.575 |
All dimensions are in inches. Overall length (L) ranges from 4.00 inches for smaller taps to 6.00 inches for the largest sizes. Thread length (l) is 1.50 inches for taps up to 1.510 inch diameter and 2.00 inches for larger sizes. Square length (l2) increases with tap size from 0.88 inches to 1.75 inches.
Where to find related tolerances and thread limits
For tolerances on these tap dimensions, see USCTI Table 302. For standard thread limits and tolerances for Unified Inch Screw Threads, see Tables 327A. For standard thread limits and tolerances for Metric Threads, see Table 337 and 341. For eccentricity tolerances of tap elements, see Table 317.
Source and updates
Source: taylortool.com engineering data. Reviewed September 2026.