61
NPT
Nominal
Diameter
Tapping
Drill Size (mm)
TPI
1/8
1/4
3/8
1/2
3/4
1"
1-1/4
1-1/2
2"
27
18
18
14
14
11-1/2
11-1/2
11-1/2
11-1/2
8.4
11.0
14.25
17.5
23.0
29.0
37.5
43.5
55.5
Fluteless Taps
Fluteless taps are used for cold forming threads in ductile materials
and have the following advantages.
(a) Increased strength and tap life resulting from:
(i)
Elimination of flutes which reduce the shear strength of
the tap.
(ii) The lack of cutting edges which, in a conventional tap,
wear and break down.
(iii) The lack of chips, which sometimes causes jamming.
(b) Better blind hole tapping due to the lack of chips and problems
relating to chip removal.
(c) Higher productivity due to faster tapping speeds.
(d) Stronger threads.
The grain fibres of the metal are not cut, but displaced, to form the
threads, which are stronger than cut threads. It is accepted that a
60% cold formed thread is as strong as a 75% cut thread.
FLUTELESS TAP
STRONGER THREAD
GRAIN FIBRE OF
METAL UNBROKEN
BURNISHED THREAD
NO CHIPS
