Pulley taps with ground threads are manufactured to MCTI Table 310 specifications for fractional sizes from 1/4 to 3/4 inch. These taps feature an internal center in the thread end and are made to H3 limits as shown in Table 327. The shank diameter is approximately equal to the maximum major diameter for each size, and the square dimension equals 0.75 times the shank diameter to the nearest 0.001 inch.
What are the standard dimensions for pulley taps?
Pulley tap dimensions include overall length (L), thread length (l), neck length (l1), square length (l2), length of close tolerance shank section (l4), shank diameter (d1), and size of square (a). The table below lists all dimensions in inches for fractional sizes.
| Nominal Fractional Diameter (Inches) | Overall Length L | Thread Length l | Neck Length l1 | Square Length l2 | Length of Shank Close Tol. Section l4 | Shank Diameter d1 | Size of Square a |
|---|---|---|---|---|---|---|---|
| 1/4 (.2500) | 6, 8 | 1.00 | .38 | .31 | 1.50 | .2550 | .191 |
| 5/16 (.3125) | 6, 8 | 1.13 | .38 | .38 | 1.56 | .3180 | .238 |
| 3/8 (.3750) | 6, 8, 10 | 1.25 | .38 | .44 | 1.63 | .3810 | .286 |
| 7/16 (.4375) | 6, 8 | 1.44 | .44 | .50 | 1.69 | .4440 | .333 |
| 1/2 (.5000) | 6, 8, 10, 12 | 1.66 | .50 | .56 | 1.69 | .5070 | .380 |
| 5/8 (.6250) | 6, 8, 10, 12 | 1.81 | .63 | .69 | 2.00 | .6330 | .475 |
| 3/4 (.7500) | 10, 12 | 2.00 | .75 | .75 | 2.25 | .7590 | .569 |
What tolerances apply to pulley tap dimensions?
Tolerances for pulley tap dimensions vary by element and size range. The table below specifies direction and magnitude of tolerances for each dimensional element.
| Element | Size Range | Direction | Tolerance |
|---|---|---|---|
| Overall Length (L) | 1/4 to 3/4 inc. | Plus or Minus | .063 |
| Thread Length (l) | 1/4 to 3/4 inc. | Plus or Minus | .063 |
| Neck Length (l1) | 1/4 to 3/4 inc. | See Note 1 | See Note 1 |
| Square Length (l2) | 1/4 to 3/4 inc. | Plus or Minus | .031 |
| Length of Shank (close tol) (l4) | 1/4 to 3/4 inc. | See Note 2 | See Note 2 |
| Shank Diameter (d1) | 1/4 to 3/4 inc. | Minus | .0050 |
| Square of Shank (a) | 1/4 to 1/2 inc. | Minus | .004 |
| Square of Shank (a) | 5/8 to 3/4 inc. | Minus | .006 |
Notes on pulley tap specifications
Note 1: L1 (Neck Length): neck and its length is optional with manufacturer.
Note 2: L4 (Length of Close Tolerance Shank) is minimum length which is held to eccentricity tolerances per Table 317.
General specifications
a) These taps have an internal center in the thread end.
b) These taps are made to the H3 limits shown in Table 327.
c) For eccentricity tolerances of taps elements see table 317.
d) d1 (Shank Diameter) is approximately the same as the maximum major diameter for that size.
e) a1 (Size or Square) is equal to .75 X d1 to the nearest .001 inch.
Source and updates
Source: taylortool.com engineering data. Reviewed September 2026.