GB/T 28257-2012Long shank nut taps (English PDF)

1 Scope

This standard lays down the basic requirements for long shank nut taps, among them their type, their dimensions and their designation.

This standard applies to long shank nut taps for machining general purpose threads to GB/T 192, GB/T 193, GB/T 196 and GB/T 197.

2 Normative references

The following documents are indispensable for the application of this document. For dated references only the edition cited applies; for undated references the latest edition, including any amendments, applies.

The documents listed are GB/T 192, General purpose metric screw threads - Basic profile; GB/T 193, General purpose metric screw threads - Diameter and pitch series; GB/T 196, General purpose metric screw threads - Basic dimensions; GB/T 197, General purpose metric screw threads - Tolerances; GB/T 968, Tolerances of tap threads; and GB/T 969, Technical specifications for taps.

3 Types and dimensions of the tap

3.1 The type of the tap is as shown in Figure 1 and its dimensions are given in Table 1 and Table 2. Figure 1 shows the tap in side view with the thread diameter d, the chamfer length l5, the threaded length l, the shank diameter d1 and the overall length L marked on it and, at the driving end, the square with the across-flats dimension a and the length l2, the square being shown in the section A-A.

Table 1, headed Long shank nut taps for coarse general purpose threads and given in millimetres, has a designation column, the nominal diameter d, the pitch P, then the overall length L, the threaded length l and the chamfer length l5, each of those three split into a type I and a type II column, then the shank diameter d1 and finally, under the heading square, the across-flats dimension a and the length l2. It covers the designations M3, M3.5, M4, M4.5, M5, M6, M7, M8, M9, M10, M11, M12, M14, M16, M18, M20, M22, M24, M27, M30 and M33. Many of its cells are merged over two, three or four rows, so a value cannot always be paired directly with a single designation, and the individual dimensional values are not reproduced here.

Two notes follow Table 1. Note 1: type I is the short chamfer tap and type II is the long chamfer tap. Note 2: the chamfer length l5 given in the table is a recommended dimension.

Table 2, headed Long shank nut taps for fine general purpose threads and given in millimetres, has the same column layout as Table 1. It covers the designations from M3x0.35 up to M45x3, listing for each nominal diameter the fine pitches offered. Its cells are merged in the same way as those of Table 1 and the individual dimensional values are not reproduced here.

In the M11 rows of Table 2 the designation and the pitch do not agree: the row designated M11x0.75 carries the pitch P = 1 and the row designated M11x1 carries the pitch P = 0.75. The two pitch values appear to have been interchanged in the printed table. They are reported here as they are printed.