scope:

This specification covers regular (with conventional-chamfered ends) and spiral-pointed (gun) high-speed steel handtaps with ground threads for machine screw, fractional size, and metric spark-plug threads.

The pitch-diameter limits of the American National taps specified herein reflect the unification of screw threads as adopted in the interest of International Standardization. It will be noted that all type I and type II taps are still listed as NC, NF, NS, etc. rather than under the Unified Screw Thread designation, i.e., UNC, UNF and UNS. In American practice there has been no change in the tap thread form and the present form will be satisfactory for cutting Unified internal threads if proper selection is made as to pitch-diameter limits.

This specification does not include all types and series of taps indicated by the title of this specification or which are commercially available, but are intended to cover only the types, styles, series and classes, which are generally used by the Federal Government.

-The taps shall conform to the following types, series, L or H limit numbers, and styles as specified (see 6.1):

Type I. -Taps, machine-screw and fractional sizes.

Series A. -Coarse-thread series (NC).

Series B. -Fine-thread series (NF).

Series C. -Special threads (NS).

Series D. -Extra-fine thread series (NEF).

Series E. -8-pitch series (8N).

Series F. -12-pitch series (12N).

Series G. -16-pitch series (16N)

Type II. -Taps, spiral-pointed, machine screw and fractional sizes.

Series A. -Coarse-thread series (NC).

Series B. -Fine-thread series (NF).

Type III. -Taps, having metric-form thread, (spark plug sizes only).

Type I and type II taps shall be of the following pitch diameter limits as specified (see 6.1):

L1.limit.

H1 limit.

H2 limit.

H3 limit.

H4 limit.

H5 limit.

H6 limit.

H7 limit.

H8 limit.

H9 limit.

H10 limit.

H11 limit.

H12 limit.

Taps shall be of the following styles as specified (see 6.1):

Style a-Taper tap¹.

Style b-Plug tap.

Style c-Bottoming tap.