USCTI Table 317 specifies eccentricity tolerances for tap elements when tested on dead centers, covering ground thread taps in inch, pipe, and metric sizes. The table provides both eccentricity and total indicator variation (t.i.v.) values for five tap elements: square, shank, major diameter, pitch diameter, and chamfer. Tolerances range from 0.0005 inch eccentricity for smaller taps to 0.004 inch for larger squares.

What eccentricity tolerances apply to tap elements?

Eccentricity tolerances for tap elements depend on the element type and tap size range. The table below lists tolerances for ground thread taps tested on dead centers, with values given for both eccentricity and total indicator variation to avoid misunderstanding.

*t.i.v. = Total indicator variation. Figures are given for both eccentricity and total indicator variation to avoid misunderstanding.

**Chamfer should preferably be inspected by light projection to avoid errors due to indicator contact points dropping into the thread grooves.

What is total indicator variation?

Total indicator variation (t.i.v.) is the full range of indicator movement when measuring eccentricity on dead centers. The t.i.v. values in the table are exactly double the eccentricity values, and both are provided to avoid misunderstanding in measurement reporting.

How should tap chamfer eccentricity be inspected?

Chamfer should preferably be inspected by light projection to avoid errors due to indicator contact points dropping into the thread grooves. This method prevents false readings that can occur when a mechanical indicator contacts the chamfer surface.

Surface treatment abbreviations

The following abbreviations are used for tap surface treatments:

Source and updates

Source: taylortool.com engineering data. Reviewed September 2026.