Taps technical information

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Terminology

Flute geometries

Chamfer forms/centres

Formulae

Hardness vs tensile strength

Steel and solid carbide

Coatings

Troubleshooting

Drill sizes

Tap Tolerance

Tolerance Table

Taps terminology

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Taps terminology

Flute geometries

STRAIGHT FLUTES

These taps are used on steels with normal strength and toughness (R=750 N/mm2) as well as on short-chipping abrasive materials (grey cast iron, bronze, etc.).

STRAIGHT FLUTES

SPIRAL FLUTES, 15° RIGHTHAND SPIRAL

These taps improve chip evacuation and are well suited when tapping blind holes of medium depth on tough materials.

SPIRAL FLUTES, 15° RIGHTHAND SPIRAL

SPIRAL FLUTES, 40° RIGHTHAND SPIRAL

The high helix angle ensures the evacuation of chips from deep blind holes.

SPIRAL FLUTES, 40° RIGHTHAND SPIRAL

SPIRAL FLUTES, 40° RIGHTHAND SPIRAL, FOR LIGHT ALLOYS

The large flutes and high helix angle ensure efficient chip removal on long-chipping light alloys such as aluminium.

SPIRAL FLUTES, 40° RIGHTHAND SPIRAL, FOR LIGHT ALLOYS

STRAIGHT FLUTES WITH INTERRUPTED THREADS

For tapping soft and mild materials such as iron, aluminium etc. The interrupted threads avoid chips sticking to the thread flanks and consequent damage of the tap.

STRAIGHT FLUTES WITH INTERRUPTED THREADS

SPIRAL POINT

The spiral point or gun nose is produced by a high helix angle combined with an increased rake angle in the front area of the tap. This design ensures spontaneous chip evacuation in the feed direction.
This geometry is suitable when tapping through holes on materials which produce continuous chips.

SPIRAL POINT

FORMING TAPS WITHOUT OIL GROOVES

These tools produce threads through plastic deformation of the workpiece material. No chips are produced during the tapping process.

FORMING TAPS WITHOUT OIL GROOVES

FORMING TAPS WITH OIL GROOVES

The oil grooves improve lubrication in the chamfer area making these taps suitable for threading deep holes.

FORMING TAPS WITH OIL GROOVES

Types of chamfer forms and centres

The types of chamfer are defined in standards DIN 2175 and DIN 2197 for forming taps and cutting taps, respectively.

  Form A Form B Form C Form D Form E Form F
Chamfer form and length Form A Form B Form C Form D Form E Form F
Flute type Tap with straight flutes Tap with straight flutes and spiral point Tap with straight flutes Tap with 15° right hand spiral Tap with 40° right hand spiral
Tap with 45° right hand spiral Forming tap without oil grooves Forming tap with oil grooves
Tap with 15° left hand spiral Tap with 40° right hand spiral Tap with 45° right hand spiral Forming tap without oil grooves Forming tap without oil grooves Forming tap with oil grooves

The tap manufacturer, according to the diameter and the application, defines the types of centres. Types of centre and chamfer are generally combined together as in the following table, but for specific applications exceptions are possible.

    Form A Form B Form C Form D Form E
Male centre

Male centre
ISO Metric coarse thread - DIN 13 M2 ≤ Ø ≤ M8 M2 ≤ Ø ≤ M8 M2 ≤ Ø ≤ M8 M2 ≤ Ø ≤ M8 -
ISO Metric fine thread - DIN 13 M2 ≤ Ø ≤ M6 M4 ≤ Ø ≤ M6 M2 ≤ Ø ≤ M6 M5 ≤ Ø ≤ M6 -
Unified coarse thread - UNC ASME - B1.1 Nr.2-56 ≤ Ø ≤ 1/4"-18 Nr.2-56 ≤ Ø ≤ 1/4"-18 Nr.2-56 ≤ Ø ≤ 1/4"-18 Nr.2-56 ≤ Ø ≤ 1/4"-18 -
Unified fine thread - UNF ASME - B1.1 Nr.2-64 ≤ Ø ≤ 1/4"-28 Nr.2-64 ≤ Ø ≤ 1/4"-28 Nr.2-64 ≤ Ø ≤ 1/4"-28 - -
Whitworth pipe thread - EN ISO 228 - - - - -
Half centre

Half centre
ISO Metric coarse thread - DIN 13 M8 < Ø ≤ M10 M8 < Ø ≤ M10 M8 < Ø ≤ M10 M8 < Ø ≤ M10 -
ISO Metric fine thread - DIN 13 M6 < Ø ≤ M10 M6 < Ø ≤ M10 M6 < Ø ≤ M10 M6 < Ø ≤ M10 -
Unified coarse thread - UNC ASME - B1.1 5/16"-18 ≤ Ø ≤ 3/8"-16 5/16"-18 ≤ Ø ≤ 3/8"-16 5/16"-18 ≤ Ø ≤ 3/8"-16 - -
Unified fine thread - UNF ASME - B1.1 5/16"-24 ≤ Ø ≤ 3/8"-24 5/16"-24 ≤ Ø ≤ 3/8"-24 5/16"-24 ≤ Ø ≤ 3/8"-24 - -
Whitworth pipe thread - EN ISO 228 Ø = 1/8"-28 Ø = 1/8"-28 Ø = 1/8"-28 - -
Female centre

Female centre
ISO Metric coarse thread - DIN 13 Ø > M10 Ø > M10 Ø > M10 Ø > M10 ALL
ISO Metric fine thread - DIN 13 Ø > M10 Ø > M10 Ø > M10 Ø > M10 ALL
Unified coarse thread - UNC ASME - B1.1 Ø ≥ 7/16"-14 Ø ≥ 7/16"-14 Ø ≥ 7/16"-14 Ø ≥ 5/16"-18 -
Unified fine thread - UNF ASME - B1.1 Ø ≥ 7/16"-20 Ø ≥ 7/16"-20 Ø ≥ 7/16"-20 - -
Whitworth pipe thread - EN ISO 228 Ø ≥ 1/4"-19 Ø ≥ 1/4"-19 Ø ≥ 1/4"-19 - -

Formulae

Parameter Formula Unit of Measurement
Cutting speed
Vc= N · π · d1
1000
m
min
Rotational speed
N= 1000 · Vc
π · d1
revolutions
min
Torque (*)
Mt= Kc · p2 · z0,6 · d1
104
N · m
Spindle power
P= Mt · 2 · π · N
60
W
Nominal diameter d1 mm
Feed p · N
mm
min
p Thread pitch mm
z Number of flutes -
Kc Cutting force coefficient
(function of the material and of tap wear)
N
mm2
M.G. Kc
[N/mm2]
P.1 1300
P.2 1400
P.3 1400
P.4 1600
P.5 1700
P.6 2000
P.7 1400
M.1 1600
M.2 1800
K.1 1100
K.2 1500
K.3 1600
N.1 600
N.2 800
N.3 900
N.4 1000
N.5 700
N.6 850
N.7 900
N.8 2500
N.9 400
N.10 500
S.1 1200
S.2 1900
S.3 1300
S.4 2400

Conversion table hardness vs tensile strength

Tensile Strength Hardness
R
[N/mm2]
HB
Brinell
HRC
Rockwell C
HV
Vickers
3400 700 68 1008
3120 688 67 955
2960 676 66 920
2890 670 65 885
2770 659 64 850
2240 650 63 826
2190 635 62 797
2140 627 61 772
2100 613 60 746
2050 600 59 720
2010 587 58 693
1970 574 57 666
1930 561 56 646
1890 548 55 623
1850 536 54 604
1810 524 53 585
1780 512 52 567
1730 500 51 549
1680 488 50 528
1630 476 49 513
1590 464 48 497
1560 453 47 482
1520 442 46 468
1480 430 45 453
1440 419 44 440
Tensile Strength Hardness
R
[N/mm2]
HB
Brinell
HRC
Rockwell C
HV
Vickers
1400 408 43 427
1360 398 42 416
1320 389 41 404
1300 377 40 391
1260 367 39 381
1230 357 38 371
1190 347 37 357
1150 337 36 345
1120 327 35 332
1100 319 34 323
1060 309 33 314
1040 301 32 304
1010 294 31 296
980 286 30 288
960 279 29 280
940 272 28 273
910 265 27 266
890 259 26 259
870 253 25 253
850 247 24 247
830 241 23 241
810 235 22 235
790 230 21 230
770 225 20 225

High speed steel and solid carbide for Taps

Vergnano Designation Designation according to
ISO 11054
Hardness Toughness Applications Structure
(500x)
HSS HSS Used exclusively for hand taps (except A100). HSS steel structure
HSSE HSS-E For general applications. HSSE steel structure
HSSK HSS-E-PM Used in applications where a compromise between high hardness and high toughness is needed. HSSK steel structure
HSSZ HSS-E-PM For applications where extremely high performance and productivity are requested. HSSZ steel structure
HSSP HSS-E-PM For tough materials and extreme applications. HSSP steel structure
HM - - For heat-treated steels and abrasive materials. HM steel structure

Coatings - Properties

Type of coating/treatment Structure Hardness Friction coefficient Oxidation temperature Features
TiN Mono-layer Wear resistance
TiCN Mono-layer Wear resistance
TiX2 Multi-layer Oxidation and wear resistance, chip evacuation
TiH1 Multi-layer Oxidation and wear resistance, chip evacuation
CrN Mono-layer Oxidation and wear resistance
V-MAXX Mono-layer Oxidation and wear resistance
VAP Surface oxidation - Chip evacuation
NiTR Surface hardening Wear resistance

Coatings - Applications

COATINGS RECOMMENDED FOR CUTTINGS TAPS TiN TiCN TiX2 TiH1 CrN V-MAXX VAP NiTR
ISO Material Group Application Coating *
P Steel P.1 Mild / magnetic steel          
P.2 Construction steel, case hardening steel          
P.3 Carbon steel, alloyed steel            
P.4 Alloyed steel / tempered Steel          
P.5 Alloyed steel / tempered Steel          
P.6 Alloyed steel / high strength steel          
P.7 Ferritic stainless steel, martensitic stainless steel, precipitation hardening          
M Stainless
Steel
M.1 Austenitic stainless steel          
M.2 Ferritic+austenitic (Duplex)          
K Cast iron K.1 Grey cast iron          
K.2 Nodular cast iron, malleable cast iron, tempered cast iron            
K.3 Austempered ductile iron (ADI)              
NA Aluminium
Aluminium alloys
N.1 Pure aluminium            
N.2 Aluminium wrought and die cast alloys with Si < 0.5% (long chipping)          
N.3 Aluminium wrought and die cast alloys with Si < 10% (mean chipping)          
N.4 Aluminium die cast alloys with Si > 10% (short chipping)          
Copper
Copper Alloys
Brass
Bronze
N.5 Pure copper            
N.6 Copper alloys (long chipping), soft brass          
N.7 Copper alloys (short chipping), hard brass            
N.8 High strength bronze          
Magnesium
Magnesium alloys
N.9 Pure magnesium, magnesium alloys            
N.10 High strength magnesium alloys            
S Titanium
Titanium alloys
S.1 Pure titanium            
S.2 Titanium alloys            
Nickel
Nickel alloys
S.3 Pure nickel            
S.4 Nickel alloys            
H Hardened materials H.1 Alloyed steel, Hardness HRC 44-55              
H.2 Alloyed steel, Hardness HRC 56-63              

COATINGS RECOMMENDED FOR COLD FORMING TAPS TiN TiCN V-MAXX VAP
ISO Material Group Application Coating *
P Steel P.1 Mild / magnetic steel    
P.2 Construction steel, case hardening steel    
P.3 Carbon steel, alloyed steel  
P.4 Alloyed steel / tempered Steel  
P.5 Alloyed steel / tempered Steel  
P.7 Ferritic stainless steel, martensitic stainless steel, precipitation hardening    
M Stainless
Steel
M.1 Austenitic stainless steel    
M.2 Ferritic+austenitic (Duplex)    
NA Aluminium
Aluminium alloys
N.1 Pure aluminium    
N.2 Aluminium wrought and die cast alloys with Si < 0.5% (long chipping)
N.3 Aluminium wrought and die cast alloys with Si < 10% (mean chipping)
Copper
Copper Alloys
Brass
Bronze
N.5 Pure copper    
N.6 Copper alloys (long chipping), soft brass  
S Titanium
Titanium alloys
S.1 Pure titanium      
S.2 Titanium alloys      
Nickel
Nickel alloys
S.3 Pure nickel    
S.4 Nickel alloys    

Troubleshooting

Tapping is a complex process and often the last machining operation performed on the workpiece. Therefore, incorrect or faulty tap ping can compromise the quality of the entire workpiece.

Numerous factors influence the process: cutting parameters, drilling parameters, lubrication, machine conditions. The choice of the correct tool is paramount in order to obtain high quality threads.

The following table summarises the most common problems encountered during tapping and their possible solutions.

Problem Solution
Chipped
teeth on tap
  • Choose correct tap, with lower rake angle or longer chamfer.
  • Reduce cutting speed.
  • Check drilled hole size is not too small.
  • Check tap alignment and run-out of tap on tapping attachment.
  • For deep blind holes (≥ 2,5xD) use taps with back-tapering.
Excessive
tap wear
  • Improve quality (richer emulsion, neat oil) and quantity (higher pressure) of lubrication.
  • Use correct tap, with more relief or longer chamfer if possible.
  • Choose coating suitable for specific application.
  • Use recommended cutting parameters for specific application.
Chips
clogging flutes
  • Use tap with lower spiral flute angle.
  • Choose correct tap with suitable rake angle and relief for specific application.
  • Use tap with sharp cutting edge (bright tap or vapourised tap).
Poor finish on
threaded workpiece
  • Check wear on tap. If necessary, resharpen or change tap.
  • Improve quality and quantity of lubrication.
  • Choose correct tap with suitable rake angle and relief for specific application.
  • Use recommended cutting parameters for specific application.
Built-up-edge
  • Choose correct tap with lower rake angle and/or higher relief.
  • Choose coating suitable for specific application.
  • Increase cutting speed.
  • Improve quality and quantity of lubrication.
Tap sticking
  • Choose correct tap with lower rake angle and/or higher relief.
  • Choose coating suitable for specific application.
  • Increase cutting speed.
  • Improve quality and quantity of lubrication.
Crater wear
  • Choose correct tap with lower rake angle and/or higher relief.
  • Choose coating suitable for specific application.
  • Increase cutting speed.
  • Improve quality and quantity of lubrication.
Tap breakage
  • Check drilled hole size.
  • Check alignment between tap and drilled hole.
  • Reduce cutting speed.
  • On blind holes, check that tapping depth is less than hole depth.
  • Use tapping attachment with slip clutch.
  • Use compensated tapping attachment.
Oversized thread
  • Check tap tolerance is compatible with requested workpiece (nut) tolerance.
  • Choose correct tap with suitable rake angle and relief for specific application.
  • Reduce feed rate (revs x pitch) or use rigid / synchronous tapping attachment.
  • Reduce cutting speed.
  • Check tap alignment and that workpiece is fastened steadily.
  • Remove clogged chips from flutes.
Undersized thread
  • Check drilled hole size is not too small.
  • Check tap tolerance is compatible with requested workpiece (nut) tolerance.
  • Use coated tap to avoid tap sticking.
  • On forming taps, use slightly larger drilled hole size.
  • Check wear on tap. If necessary, resharpen or change tap.
  • Choose correct tap with higher rake angle and relief.
  • Use rigid / synchronous tapping attachment.
  • Improve quality and quantity of lubrication.
Excessive power
requirement
  • On high strength materials, increase drilled hole size.
  • Check wear on tap. If necessary, resharpen or change tap.
  • Choose correct tap with higher rake angle and relief.
  • Improve quality and quantity of lubrication.

Drill sizes cutting Taps

ISO Metric coarse thread - DIN 13
D Pitch
[mm]
Maximum core
diam.
(tol. 6H)
[mm] D1
Drill size *
[mm]
M1 0,25 0,785 (1) 0,75
1,1 0,25 0,885 (1) 0,85
1,2 0,25 0,985 (1) 0,95
1,4 0,3 1,142 (1) 1,1
1,6 0,35 1,321 1,25
1,7 (3) 0,35 1,421 1,35
1,8 0,35 1,521 1,45
2 0,4 1,679 1,6
2,2 0,45 1,838 1,75
2,3 (3) 0,4 1,938 1,9
2,5 0,45 2,138 2,05
2,6 (3) 0,45 2,238 2,1
3 0,5 2,599 2,5
3,5 0,6 3,01 2,9
4 0,7 3,422 3,3
4,5 0,75 3,878 3,7
5 0,8 4,334 4,2
6 1 5,153 5
7 1 6,153 6
8 1,25 6,912 6,8
9 1,25 7,912 7,8
10 1,5 8,676 8,5
11 1,5 9,676 9,5
12 1,75 10,441 10,2
14 2 12,21 12
16 2 14,21 14
18 2,5 15,744 15,5
20 2,5 17,744 17,5
22 2,5 19,744 19,5
24 3 21,252 21
27 3 24,252 24
30 3,5 26,771 26,5
33 3,5 29,771 29,5
36 4 32,27 32
39 4 35,27 35
42 4,5 37,799 37,5
45 4,5 40,799 40,5
48 5 43,297 43
52 5 47,297 47
56 5,5 50,796 50,5
60 (3) 5,5 54,796 54,5
64 (3) 6 58,305 58
68 (3) 6 62,305 62
       
       
ISO Metric fine thread - DIN 13
D Pitch
[mm]
Maximum core
diam.
(tol. 6H)
[mm] D1
Drill size *
[mm]
  D Pitch
[mm]
Maximum core
diam.
(tol. 6H)
[mm] D1
Drill size *
[mm]
M2 (3) 0,25 1,774 (2) 1,75   M25 1 24,153 24
2,3 (3) 0,25 2,085 2,05   25 1,5 23,676 23,5
2,5 0,35 2,221 2,15   25 2 23,21 23
3 0,35 2,721 2,65   26 1,5 24,676 24,5
3,5 0,35 3,221 3,15   27 1 26,153 26
4 0,5 3,599 3,5   27 1,5 25,676 25,5
4,5 0,5 4,099 4   27 2 25,21 25
5 0,5 4,599 4,5   28 1 27,153 27
5,5 0,5 5,099 5   28 1,5 26,676 26,5
6 0,75 5,378 5,2   28 2 26,21 26
7 0,75 6,378 6,2   30 1 29,153 29
8 0,75 7,378 7,2   30 1,5 28,676 28,5
8 1 7,153 7   30 2 28,21 28
9 0,75 8,378 8,2   30 3 27,252 27
9 1 8,153 8   32 1,5 30,675 30,5
10 0,75 9,378 9,2   32 2 30,21 30
10 1 9,153 9   33 1,5 31,676 31,5
10 1,25 8,912 8,8   33 2 31,21 31
11 0,75 10,378 10,2   33 3 30,252 30
11 1 10,153 10   35 1,5 33,676 33,5
12 (3) 0,75 11,378 11,2   36 1,5 34,676 34,5
12 1 11,153 11   36 2 34,21 34
12 1,25 10,912 10,8   36 3 33,252 33
12 1,5 10,676 10,5   38 1,5 36,676 36,5
14 1 13,153 13   39 1,5 37,676 37,5
14 1,25 12,912 12,8   39 2 37,21 37
14 1,5 12,676 12,5   39 3 36,252 36
15 1 14,153 14   40 1,5 38,676 38,5
15 1,5 13,676 13,5   40 2 38,21 38
16 1 15,153 15   40 3 37,252 37
16 1,5 14,676 14,5   42 1,5 40,676 40,5
17 1 16,153 16   42 2 40,21 40
17 1,5 15,676 15,5   42 3 39,252 39
18 1 17,153 17   45 1,5 43,676 43,5
18 1,5 16,676 16,5   45 2 43,21 43
18 2 16,21 16   45 3 42,252 42
20 1 19,153 19   48 1,5 46,676 46,5
20 1,5 18,676 18,5   48 2 46,21 46
20 2 18,21 18   48 3 45,252 45
22 1 21,153 21   50 1,5 48,676 48,5
22 1,5 20,676 20,5   50 2 48,21 48
22 2 20,21 20   50 3 47,252 47
24 1 23,153 23   52 1,5 50,676 50,5
24 1,5 22,676 22,5   52 2 50,21 50
24 2 22,21 22   52 3 49,252 49

ISO Metric coarse thread - DIN 8140 part 2
D Drill size *
[mm]
EG-M 3 3,15
4 4,2
5 5,25
6 6,3
8 8,4
10 10,5
12 12,5
14 14,5
16 16,5
 
8-UN thread - ASME B1.1
D Pitch
[T.P.I]
Maximum
core diam.
(class. 3B)
[mm] D1
Drill size *
[mm]
1 1/8" 8 25,519 25,4
1 1/4" 8 28,694 28,6
1 3/8" 8 31,869 31,8
1 1/2" 8 35,044 35
1 5/8" 8 38,219 38,1
1 3/4" 8 41,394 41,3
1 7/8" 8 44,569 44,5
2" 8 47,744 47,7
       

Unified coarse thread - UNC ASME - B1.1
D Pitch
[T.P.I]
Maximum
core diam.
(class. 3B)
[mm] D1
Drill size *
[mm]
Nr. 1 64 1,582 1,55
Nr. 2 56 1,872 1,85
Nr. 3 48 2,146 2,1
Nr. 4 40 2,385 2,35
Nr. 5 40 2,697 2,65
Nr. 6 32 2,896 2,85
Nr. 8 32 3,528 3,5
Nr. 10 24 3,95 3,9
Nr. 12 24 4,59 4,5
1/4" 20 5,25 5,1
5/16" 18 6,68 6,6
3/8" 16 8,082 8
7/16" 14 9,441 9,4
1/2" 13 10,881 10,8
9/16" 12 12,301 12,2
5/8" 11 13,693 13,5
3/4" 10 16,624 16,5
7/8" 9 19,52 19,5
1" 8 22,344 22,25
1 1/8" 7 25,082 25
1 1/4" 7 28,258 28
1 3/8" 6 30,851 30,75
1 1/2" 6 34,026 34
1 3/4" 5 39,56 39,5
2" 4,5 45,367 45
  
Unified fine thread - UNF ASME - B1.1
D Pitch
[T.P.I]
Maximum
core diam.
(class. 3B)
[mm] D1
Drill size *
[mm]
Nr. 0 80 1,306 1,25
Nr. 1 72 1,613 1,55
Nr. 2 64 1,913 1,85
Nr. 3 56 2,197 2,15
Nr. 4 48 2,459 2,4
Nr. 5 44 2,741 2,7
Nr. 6 40 3,012 2,95
Nr. 8 36 3,597 3,5
Nr. 10 32 4,168 4,1
Nr. 12 28 4,717 4,6
1/4" 28 5,563 5,5
5/16" 24 6,995 6,9
3/8" 24 8,565 8,5
7/16" 20 9,947 9,9
1/2" 20 11,524 11,5
9/16" 18 12,969 12,9
5/8" 18 14,554 14,5
3/4" 16 17,546 17,5
7/8" 14 20,493 20,4
1" 12 23,363 23,25
1 1/8" 12 26,538 26,5
1 1/4" 12 29,713 29,5
1 3/8" 12 32,888 32,75
1 1/2" 12 36,063 36
       

Whitworth thread - BS 84
D Pitch
[T.P.I]
Maximum
core diam.
[mm] D1
Drill size
[mm]
3/32" 48 1,912 1,9
1/8" 40 2,591 2,55
5/32" 32 3,214 3,2
3/16" 24 3,744 3,7
7/32" 24 4,539 4,5
1/4" 20 5,156 5,1
5/16" 18 6,589 6,5
3/8" 16 7,988 7,9
7/16" 14 9,332 9,25
1/2" 12 10,589 10,5
9/16" 12 12,177 12
5/8" 11 13,559 13,5
3/4" 10 16,485 16,4
7/8" 9 19,355 19,25
1" 8 22,149 22
1 1/8" 7 24,831 24,75
1 1/4" 7 28,006 27,75
1 3/8" 6 30,528 30,3
1 1/2" 6 33,703 33,5
1 5/8" 5 35,961 35,5
1 3/4" 5 39,136 39
1 7/8" 4,5 41,702 41,5
2" 4,5 44,877 44,5
2 1/4" 4 50,465 50
2 1/2" 4 56,815 56,3
2 3/4" 3,5 62,182 61,5
3" 3,5 68,532 68
  
Whitworth pipe thread - EN ISO 228
D Pitch
[T.P.I]
Maximum
core diam.
[mm] D1
Drill size *
[mm]
1/8" 28 8,848 8,8
1/4" 19 11,89 11,8
3/8" 19 15,395 15,25
1/2" 14 19,172 19
5/8" 14 21,128 21
3/4" 14 24,658 24,5
7/8" 14 28,418 28,25
1" 11 30,931 30,75
1 1/8" 11 35,579 35,5
1 1/4" 11 39,592 39,5
1 3/8" 11 42,005 41,9
1 1/2" 11 45,485 45,25
1 3/4" 11 51,428 51
2" 11 57,296 57
2 1/4" 11 63,392 63,3
2 3/8" 11 67,08 67
2 1/2" 11 72,866 72,8
2 3/4" 11 79,216 79,1
3" 11 85,566 85,5
3 1/4" 11 91,662 91,5
3 1/2" 11 98,012 98
3 3/4" 11 104,362 104
4" 11 110,712 110,5
       
       
       
       
  
Rp thread (BSPP) - DIN EN 10226-1
D Pitch
[T.P.I]
Maximum
core diam.
[mm] D1
Drill size *
[mm]
1/8” 28 8,637 8,6
1/4” 19 11,549 11,5
3/8” 19 15,054 15
1/2” 14 18,773 18,5
3/4” 14 24,259 24
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       

Rc (BSPT) - Conical gas thread (BSPT), taper 1:16 - BS 21 and DIN EN 10226-2
D Pitch
[T.P.I]
Drill size
[mm] D1
t1 [mm]
1/16" 28 6,2 11,9
1/8" 28 8,2 11,9
1/4" 19 11 17,7
3/8" 19 14,5 18,1
1/2" 14 18 24
3/4" 14 23,5 25,3
1" 11 29,5 30,6
1 1/4" 11 38 32,9
1 1/2" 11 44 32,9
2" 11 55,5 37,2
 
NPT - National pipe thread, taper 1:16 - ANSI B1.20.1
D Pitch
[T.P.I]
Drill size
[mm] D1
t1 [mm]
1/16" 27 6,15 12
1/8" 27 8,5 12
1/4" 18 11 17,5
3/8" 18 14,5 17,6
1/2" 14 17,85 22,9
3/4" 14 23,2 23
1" 11 1/2 29 27,4
1 1/4" 11 1/2 37,8 28,1
1 1/2" 11 1/2 44 28,4
2" 11 1/2 56 28,4
 
NPTF - Dryseal National pipe thread, taper 1:16 - ANSI B1.20.3
D Pitch
[T.P.I]
Drill size
[mm] D1
t1 [mm]
1/16" 27 6,15 12
1/8" 27 8,5 12
1/4" 18 11 17,5
3/8" 18 14,5 17,6
1/2" 14 17,8 22,9
3/4" 14 23 23
1" 11 1/2 29 27,4
1 1/4" 11 1/2 37,8 28,1
1 1/2" 11 1/2 43,8 28,4
2" 11 1/2 56 28,4

Drill sizes forming Taps

In order to obtain the requested tolerance, the formation of a complete internal thread and guarantee the tap tool life, it is important to respect the drill hole diameters and their tight tolerances.
The core diameter of the internal thread obtained by forming is not only a function of the drill hole diameter but also depends on the workpiece material properties. For this reason the tolerance on the core diameter is 7H compared to 6H for cutting taps.
For more detailed information see the DIN 13-50 standard.

ISO Metric coarse thread - DIN 13
D Pitch
[mm]
Drill size
[mm]
M 2 0,4   1,85 ± 0,03
2,5 0,45   2,30 ± 0,03
3 0,5   2,80 ± 0,03
3,5 0,6   3,25 ± 0,03
4 0,7   3,70 ± 0,03
5 0,8   4,65 ± 0,03
6 1   5,55 ± 0,05
8 1,25   7,40 ± 0,05
10 1,5   9,30 ± 0,05
12 1,75 11,20 ± 0,05
14 2 13,10 ± 0,05
16 2 15,10 ± 0,05
18 2,5 16,90 ± 0,05
20 2,5 18,90 ± 0,05
24 3 22,70 ± 0,05
27 3 25,70 ± 0,05
30 3,5 28,45 ± 0,05
ISO Metric fine thread - DIN 13
D Pitch
[mm]
Drill size
[mm]
M 3 0,35   2,85 ± 0,03
4 0,5   3,80 ± 0,03
5 0,5   4,80 ± 0,03
6 0,75   5,65 ± 0,03
8 1   7,55 ± 0,05
10 1   9,55 ± 0,05
10 1,25   9,40 ± 0,05
12 1 11,55 ± 0,05
12 1,25 11,40 ± 0,05
12 1,5 11,30 ± 0,05
14 1,25 13,40 ± 0,05
14 1,5 13,30 ± 0,05
16 1,5 15,30 ± 0,05
18 1,5 17,30 ± 0,05
20 1,5 19,30 ± 0,05
     
     
Whitworth pipe thread - EN ISO 228
D Pitch
[T.P.I]
Drill size
[mm]
  G 1/8" 28    9,25 ± 0,05
      1/4" 19 12,50 ± 0,05
      3/8" 19 16,00 ± 0,05
      1/2" 14 20,00 ± 0,05
      3/4" 14 25,50 ± 0,05
      1" 11 32,00 ± 0,05
     
     
     
     
     
     
     
     
     
     
     


Other drill sizes = theoretical flank diameter + pitch/5

Cutting Taps tolerance range

Tolleranze maschi ad asportazione

Forming Taps tolerance range

Tolleranze maschi ad asportazione Standard fit for a thread corresponds to tolerance class ISO 2/6H. For more precise fits, without allowance on thread flank, tolerance class ISO 1/4H must be chosen. ISO 3/6G is used in case of loose fits, with large allowance, which is often required for subsequent coatings.

Between classes 6H and 6G, as well as between classes 6G and 7G, tap manufacturers produce taps with tolerance 6HX and 6GX. These taps are used for tapping abrasive materials, such as cast iron or Al-Si alloys, in order to increase their tool life. Another important application is on forming taps, which create the thread by plastic deformation and not by cutting. In this case, due to the elastic return of the material, in order to obtain a thread 6H tolerance, a 6HX tap must be used.

The tolerances described above are collected in the European standard EN 22857.

Tolerance Table

Nominal diameter (mm) Pitch (mm) Limits on pitch diameter (μm)*
Class
> 4H (ISO1) 6H (ISO2) 6G (ISO3) 7G
0,99 1,4 0,2 + 15 - - -
+ 5 - - -
0,25 + 17 - - -
+ 6 - - -
0,3 + 18 + 30 - -
+ 6 + 18 - -
1,4 2,8 0,2 + 16 - - -
+ 5 - - -
0,25 + 18 - - -
+ 6 - - -
0,35 + 20 + 34 - -
+ 7 + 20 - -
0,4 + 21 + 36 - -
+ 7 + 21 - -
0,45 + 23 + 38 - -
+ 8 + 23 - -
2,8 5,6 0,35 + 21 + 36 - -
+ 7 + 21 - -
0,5 + 24 + 40 + 56 + 70
+ 8 + 24 + 40 + 55
0,6 + 27 + 45 + 63 + 81
+ 9 + 27 + 45 + 63
0,7 + 29 + 48 + 67 + 86
+ 10 + 29 + 48 + 67
0,75 + 29 + 48 + 67 + 86
+ 10 + 29 + 48 + 67
0,8 + 30 + 50 + 70 + 90
+ 10 + 30 + 50 + 70
5,6 11,2 0,75 + 32 + 53 + 74 -
+ 11 + 32 + 53 -
1 + 35 + 59 + 83 + 107
+ 12 + 35 + 59 + 83
1,25 + 38 + 63 + 88 + 113
+ 13 + 38 + 63 + 88
1,5 + 42 + 70 + 98 + 126
+ 14 + 42 + 70 + 98
11,2 22,4 1 + 38 + 63 + 88 + 113
+ 13 + 38 + 63 + 88
1,25 + 42 + 70 + 98 + 126
+ 14 + 42 + 70 + 98
1,5 + 45 + 75 + 105 + 135
+ 15 + 45 + 75 + 105
1,75 + 48 + 80 + 112 + 144
+ 16 + 48 + 80 + 112
2 + 51 + 85 + 119 + 153
+ 17 + 51 + 85 + 119
2,5 + 54 + 90 + 126 + 162
+ 18 + 54 + 90 + 126
22,4 45 1 + 40 + 66 + 92 + 118
+ 13 + 40 + 66 + 92
1,5 + 48 + 80 + 112 + 144
+ 16 + 48 + 80 + 112
2 + 54 + 90 + 126 + 162
+ 18 + 54 + 90 + 126
3 + 64 + 106 + 148 + 190
+ 21 + 64 + 106 + 148
3,5 + 67 + 112 + 157 + 202
+ 22 + 67 + 112 + 157
4 + 71 + 118 + 165 + 212
+ 24 + 71 + 118 + 165
4,5 + 75 + 125 + 175 + 225
+ 25 + 75 + 125 + 125
45 90 1,5 + 51 + 85 + 119 + 153
+ 17 + 51 + 85 + 119
2 + 57 + 95 + 133 + 171
+ 19 + 57 + 95 + 133
3 + 67 + 112 + 157 + 202
+ 22 + 67 + 112 + 157
4 + 75 + 125 + 175 + 225
+ 25 + 75 + 125 + 175
5 + 80 + 133 + 186 + 239
+ 27 + 80 + 133 + 186
5,5 + 84 + 140 + 196 + 252
+ 28 + 84 + 140 + 196
6 + 90 + 150 + 210 + 270
+ 30 + 90 + 150 + 210

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