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TOOLS FOR THREAD ROLLING MACHINES

 


 


 

Nut taps GH class (thread limit) selection

Tolerance class diagram for nut taps
Tolerance class diagram for nut taps

class GH normal accuracy (13µm), class A increased accuracy (10µm).
Vertical Axis - Average Diameter Tolerance

 

The accuracy class of the nut tap is determined by the tolerances (1, 2, 3B, 2B etc.) on the internal thread

 

Table 1. Metric thread (M)

Thread Specification Pitch Tap thread tolerance
Class 1 internal thread Class 2 internal thread
M3   M4  M4.5  M5  M5.5 0.5 GH3 GH4 GH5 GH6
M3   M3.5 0.35 GH3 GH4 GH5 GH6
M3.5 0.6 GH3 GH4 GH5 GH6
M4 0.7 GH4 GH5 GH6 GH7
M5 0.8 GH4 GH5 GH6 GH7
M6 1 GH4 GH5 GH6 GH7
M4   M4.5   M6 0.75 GH4 GH5 GH6 GH7
M7   M8   M9 1 GH4 GH5 GH6 GH7
M10  M11 0.75 GH4 GH5 GH6 GH7
M10  M11   M12 1 GH4 GH6 GH7 GH8
M8   M9   M10   M12 1.25 GH5 GH6 GH7 GH8
M10  M11   M12 1.5 GH5 GH6 GH7 GH8
M12 1.75 GH5 GH7 GH8 GH9
M14  M15   M16 1 GH5 GH6 GH7 GH8
M17  M18   M20   M22   M24    1 GH5 GH6 GH7 GH8
M14  M15   M16 1.5 GH5 GH7 GH8 GH9
M18  M20   M22   M24    1.5 GH6 GH7 GH8 GH9
M14  M16 2 GH6 GH7 GH8 GH9
M17 1.5 GH6 GH8 GH9 GH10
M18  M20   M22 2 GH6 GH8 GH9 GH10
M18  M20   M22 2.5 GH6 GH8 GH9 GH10
M24 2 GH6 GH8 GH9 GH10
M24 3 GH6 GH8 GH9 GH10

 

Table 2. American thread (U)

Thread Specification Threads per inch
(25.4 mm)
Tap thread tolerance
Class 1 internal thread Class 2 internal thread
No.5 44 GH3 GH4 GH5 GH6
No.5   No.6 40 GH3 GH4 GH5 GH6
No.8 36 GH4   GH5 GH6
No.6   No.8   No.10    32 GH4   GH5 GH6
No.10  No.12 24 GH4   GH5 GH6
No.12 28 GH4   GH5 GH6
U  1/4 20 GH4 GH5 GH6 GH7
  28 GH4   GH5 GH6
U  5/16 18 GH5 GH6 GH7 GH8
  24 GH5   GH6 GH7
U  3/8 16 GH5 GH6 GH7 GH8
  24 GH5   GH6 GH7
U  7/16 14 GH5 GH6 GH7 GH8
  20 GH5 GH6 GH7 GH8
U  1/2 13 GH6 GH7 GH8 GH9
  20 GH5 GH6 GH7 GH8
U  9/16 12 GH6 GH7 GH8 GH9
  18 GH6 GH7 GH8 GH9
U  5/8 11 GH7 GH8 GH9 GH10
  18 GH6 GH7 GH8 GH9
U  3/4 10 GH7 GH8 GH9 GH10
  16 GH6 GH7 GH8 GH9
U  7/8 9 GH7 GH8 GH9 GH10
  14 GH6 GH7 GH8 GH9
U  1" 8 GH8 GH9 GH10 GH11
  12 GH7 GH8 GH9 GH10

 

Table 3. W-Type thread

Thread Specification Threads per inch
(25.4 mm)
Tap thread tolerance
Class 1 internal thread Class 2 internal thread
W  1/8 44 GH3 GH4 GH5 GH6
W  5/32 40 GH3 GH4 GH5 GH6
W  3/24 36 GH4   GH5 GH6
W  1/4 20 GH4 GH5 GH6 GH7
W  5/16 18 GH5 GH6 GH7 GH8
W  3/8 16 GH5 GH6 GH7 GH8
W  7/16 14 GH5 GH6 GH7 GH8
W  1/2 12 GH6 GH7 GH8 GH9
W  9/16 12 GH6 GH7 GH8 GH9
W  5/8 11 GH7 GH8 GH9 GH10
W  3/4 10 GH7 GH8 GH9 GH10
W  7/8 9 GH7 GH8 GH9 GH10
W  1" 8 GH8 GH9 GH10 GH11

Notes:
1) Actual parameters of accuracy when processing materials may differ from the reference depending on specific materials and processing conditions.

2) Tables 1, 2 and 3 define the tap tolerance in 12.7 µm (0.0005") increments.


upper limit = 12.7 µm × n (n = GH number)
lower limit = upper limit - 12.7 µm

Example: GH limits GH6
upper limit: 12.7 × 6 = 77 µm,
lower limit: 77 µm - 12.7 µm (round to 13 µm) = 64 µm

 

Tapping Speed in different materials

Nut type Suitable cutting speed
(m/min)
Cutting Fluid for tapping threads in nut
cold formed nuts
mild steel 25 ~ 35 Non-water soluble cutting fluids
ordinary steel
20 ~ 30
hot forged nuts mild steel
25 ~ 35
ordinary steel 20 ~ 30
heat treated nuts 25~30HRC 25 ~ 35
30 ~ 36HRC 10 ~ 20
stainless steel nuts 15 ~ 25


Tapping speed formula for nut taps

V = π × D × N / 1000
π = 3,1416
V - cutting speed (m/min)
D - nut tap diameter (mm)
N - spindle speed (rpm)

 

Recommended Drill Hole Size for Nut Taps

Table 1. Metric Coarse Threads (M)

Thread Specification Minimum size Maximum size
Class 1 Class 2 Class 3
5H 6H 7H
M3  × 0.5 2.46 2.57 2.6 2.64
M3.5 × 0.6 2.85 2.98 3.01 3.05
M4  × 0.7 3.24 3.38 3.42 3.47
M4.5 × 0.75 3.69 3.84 3.88 3.92
M5  × 0.8 4.13 4.29 4.33 4.38
M6  × 1 4.92 5.11 5.15 5.22
M7  × 1 5.92 6.11 6.15 6.22
M8  × 1.25 6.65 6.86 6.91 6.98
M9  ×1.25 7.65 7.86 7.91 7.98
M10 × 1.5 8.38 8.61 8.68 8.75
M11 × 1.5 9.38 9.61 9.68 9.75
M12 × 1.75 10.11 10.37 10.44 10.53
M14 × 2 11.84 12.14 12.21 12.31
M16 × 2 13.84 14.14 14.21 14.31
M18 × 2.5 15.29 15.65 15.74 15.85
M20 × 2.5 17.29 17.65 17.74 17.85
M22 × 2.5 19.29 19.65 19.74 19.85
M24 × 3 20.75 21.15 21.25 21.38
M27 × 3 23.75 24.15 24.25 24.38

 

Table 2. Metric Fine Threads (MF)

Thread Specification Minimum size Maximum size
Class 1 Class 2 Class 3
5H 6H 7H
M4  × 0.5 3.46 3.57 3.6 3.64
M5  × 0.5 4.46 4.57 4.6 4.64
M6  × 0.75 5.19 5.34 5.38 5.42
M7  × 0.75 6.19 6.34 6.38 6.42
M8  × 0.75 7.19 7.34 7.38 7.42
M9  × 0.75 8.19 8.34 8.38 8.42
M8  × 1 6.92 7.11 7.15 7.22
M9  × 1 7.92 8.11 8.15 8.22
M10 × 1 8.92 9.11 9.15 9.22
M10 × 1.25 8.65 8.86 8.91 8.98
M12 × 1.25 10.65 10.86 10.91 10.98
M14 × 1.25 12.65 12.86 12.91 12.98
M12 × 1.5 10.38 10.61 10.68 10.75
M14 × 1.5 12.38 12.61 12.68 12.75
M16 × 1.5 14.38 14.61 14.68 14.75
M18 × 1.5 16.38 16.61 16.68 16.75
M20 × 1.5 18.38 18.61 18.68 18.75
M22 × 1.5 20.38 20.61 20.68 20.75
M24 × 1.5 22.38 22.61 22.68 22.75
M18 × 2 15.84 16.14 16.21 16.31
M20 × 2 17.84 18.14 18.21 18.31
M22 × 2 19.84 20.14 20.21 20.31
M24 × 2 21.84 22.14 22.21 22.31

 

Table 3. American UNC Thread

Thread Specification Minimum size Maximum size
3B 2B 1B
No. 4-40UNC 2.16 2.39 2.39
No. 5-40UNC 2.49 2.7 2.7
No. 6-32UNC 2.64 2.9 2.9
No. 8-32UNC 3.3 3.53 3.53
No.10-24UNC 3.68 3.95 3.96
No.12-24UNC 4.34 4.55 4.6
1/4-20UNC 4.98 5.25 5.26
5/16-18UNC 6.4 6.68 6.73
3/8-16UNC 7.8 8.08 8.15
7/16-14UNC 9.14 9.44 9.55
1/2-13UNC 10.59 10.88 11.02
9/16-12UNC 11.99 12.3 12.45
5/8-11UNC 13.39 13.69 13.87
3/4-10UNC 16.31 16.62 16.84
7/8-9UNC 19.18 19.51 19.76
1"-8UNC 21.97 22.34 22.61

 

Table 4. American UNF thread

Thread Specification Minimum size Maximum size
3B 2B 1B
No. 4-48UNF 2.27 2.46 2.46
No. 5-44UNF 2.55 2.74 2.74
No. 6-40UNF 2.82 3.01 3.02
No. 8-36UNF 3.4 3.6 3.61
No.10-32UNF 3.96 4.17 4.17
No.12-28UNF 4.5 4.72 4.72
1/4-28UNF 5.36 5.56 5.59
5/16-24UNF 6.78 7 7.04
3/8-24UNF 8.38 8.57 8.64
7/16-20UNF 9.73 9.95 10.03
1/2-20UNF 11.33 11.52 11.61
9/16-18UNF 12.75 12.97 13.08
5/8-18UNF 14.35 14.55 14.68
3/4-16UNF 17.32 17.55 17.68
7/8-14UNF 20.27 20.49 20.68
1"-12UNF 23.11 23.36 23.57

 

Table 5. W-Type thread

Thread Specification Minimum size Maximum size
II, III, IV
1/8 W 40 2.49 2.68
5/32 W 32 3.1 3.31
3/16 W 24 3.58 3.82
1/4 W 20 4.91 5.2
5/16 W 18 6.34 6.67
3/8 W 16 7.73 8.11
7/16 W 14 9.05 9.51
1/2 W 12 10.31 10.83
9/16 W 12 11.9 12.42
5/8 W 11 13.26 13.82
3/4 W 10 16.18 16.78
7/8 W  9 19.03 19.69
1" W  8 21.81 22.51


Tapping drill formula for nut taps:

Formula 1
drill size = D - 2 × H1 × (f1/100)
D - tap diameter
f1 = 90 % - percentage of thread engagement (in %)
H1 - thread height
H1 = 0.541266 × P
P - thread pitch

Formula 2
drill size = D - P
D - tap diameter
P - thread pitch



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