Page 238 - Fanar

i Technical Information

4.8. Classes of Machine Taps

The machine taps presented in our catalog are made in the basic class, intended for the most commonly used
internal thread tolerances, appropriate for the particular thread types: for metric thread 6H, for unified thread UNC,
UNF - 2B, for Whitworth thread BSW, BSF - "normal.” Per individual request we can manufacture the taps in other
classes.Tap classes (ie. the tolerance field of a working segment) for metric threads are unified by international
and national standards. A particular class of the tap threads allow for two or three fields of tolerance (see drawing
and table below.)

Metric internal thread

[µm]
Tap Forming Tap
8G 8G

8H 8H
7G 7G
7H 7H
6G 6G
6H 6H
5G 5G
7GX
5H 4G 5H 4G
7GX 6GX
4H 4H
6GX 7G 6HX
6HX 6G 4HX
4HX 6H
4H
D 2
Threading die
d 2
4h
Key
4h 6H
6g tolerance field of internal thread pitch
diameter
6e
tolerance field of external thread pitch
6g diameter
8e 6g
6e 6HX tolerance field of tap/forming tap

6g threading die tolerance field
8e

According to Tolerance field of internal thread
DIN 802
4H 4H 5H - - -
6H 4G 5G 6H - -
6G - - 6G 7H 8H
7G* - - - 7G 8G

*DIN 802 provides the possibility of correction the tap tolerance comparing to the standard demands in case when it is required
by the particular machining conditions, e.g. the sort of machining material. In such situation the symbol of the tap’s class with
the sign “X”, e.g. 6HX, 6GX is obligatory.
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