Taps technical information

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Terminology

Chamfer forms/centres

Coloured rings

Steel and solid carbide

Coatings

Troubleshooting

Formulae

Drill sizes

Tolerance range

Taps terminology

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Taps terminology

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.

Chamfer form and length Form A Form B Form C Form D Form E
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 25° 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

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 Ø > M10
ISO Metric fine thread - DIN 13 Ø > M10 Ø > M10 Ø > M10 Ø > M10 Ø > M10
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 - -
-
-
Removed centre

Removed centre Removed centre
ISO Metric coarse thread - DIN 13 - - - - Ø ≤ M10
ISO Metric fine thread - DIN 13 - - - - Ø ≤ M10
Unified coarse thread - UNC ASME - B1.1 - - - - -
-
-
Unified fine thread - UNF ASME - B1.1 - - - - -
Whitworth pipe thread - EN ISO 228 - - - - -

Coloured rings

While the chamfer and flutes of the tap depend on the type of hole (blind or through) to machine, other geometrical aspects such as number of flutes, rake angle, and relief of the tap are determined by the material to be machined.

In order to simplify the choice of the correct tap, some Vergnano taps have coloured rings.

Yellow ring

MACHINE TAPS for LIGHT ALLOYS

Spiral flutes with 40° right hand spiral for blind holes (Vergnano A72)

Spoglia 1
γ 
Δ1 
= increased
= normal
Orange ring

MACHINE TAPS for STEEL WITH TENSILE STRENGTH from 500 N/mm2 to 1200 N/mm2

Straight flutes with spiral point for through holes
(Vergnano A15S - A16S - A17S - A18S - A19S - A20S)

Spiral flutes with 40° right hand spiral for blind holes
(Vergnano A59S - A60S - A61S - A70S - A70SE - A71S - A76S - A159S - A701S)

Spoglia 2
γ 
Δ1 
= normal
= increased
Green ring

MACHINE TAPS for STAINLESS STEELS

Straight flutes with spiral point for through holes
(Vergnano A150)

Spiral flutes with 40° right hand spiral for blind holes
(Vergnano A170)

Spoglia 3
γ 
Δ1 
= increased
= increased
Blue ring

MACHINE TAPS for TITANIUM and TITANIUM ALLOYS

Straight flutes for blind and through holes
(Vergnano A110)

Spoglia 4
γ 
Δ1 

= normal
= highly
increased
Red ring

HAND TAPS in sets of three pieces for STEEL WITH TENSILE STRENGTH up to 1200 N/mm2

A red ring is used for these hand taps which differ from other sets because of the superior base material, HSSE instead of HSS, and the cylindrical guide on the roughing tap (Vergnano A100).
These characteristics make this tap particularly suitable for hand tapping high resistance steels.

Cylindrical guide on the roughing tap Roughing tap

High speed steel and solid carbide for Taps

Vergnano Designation

Designation according to
ISO 11054

Properties

Applications

Structure
(500x)

HSS HSS Conventional steel with normal hardness and toughness. Used exclusively for hand taps (except A100). HSS steel structure
HSSE HSS-E Conventional steel with good hardness, toughness and wear resistance. For general applications. HSSE steel structure
HSSK HSS-E-PM Powder metallurgy steel with excellent mechanical properties. Excellent substrate for coatings. Used in applications where a compromise between high hardness and high toughness is needed. HSSK steel structure
HSSZ HSS-E-PM Powder metallurgy steel with very high hardness and wear resistance. Excellent substrate for advanced coatings. For applications where extremely high performance and productivity are requested. HSSZ steel structure
HSSP HSS-E-PM Powder metallurgy steel with high alloy content and excellent mechanical properties. Excellent substrate for coatings. For tough materials and extreme applications. HSSP steel structure
HM - Grade K solid carbide with ultra-fine carbide grain size. For heat-treated steels and abrasive materials. HM steel structure

Coatings - Properties

Type of coating/treatment

Structure

Hardness HV (0,05)

Friction coefficient on steel(dry conditions)

Radial thickness [µm]

Oxidation temperature [°C]

Features

TiN
Rivestimento TiN
Mono-layer 2300 0,40 1 ÷ 5 600 Wear resistance
TiCN
Rivestimento TiCN
Mono-layer 3000 0,40 1 ÷ 5 400 Wear resistance
TiX2
Rivestimento TiX2
Multi-layer 3000 0,20 2 ÷ 6 500 Oxidation and wear resistance, chip evacuation
TiH1
Rivestimento TiH1
Multi-layer 3000 0,20 2 ÷ 6 800 Oxidation and wear resistance, chip evacuation
CRN
Rivestimento CRN
Mono-layer 1750 0,50 1 ÷ 4 700 Oxidation and wear resistance
TiAlN
Rivestimento TiAlN
Nano structured 3300 0,30 1 ÷ 6 900 Oxidation and wear resistance
ACE
Rivestimento ACE
Mono-layer 3200 0,35 1 ÷ 5 1100 Oxidation and wear resistance
Steam tempering
Vaporizzazione
Surface oxidation 400 - - 550 Chip evacuation
Nitriding
Nitrurazione
Surface hardening 1300 - - 550 Wear resistance

Coatings - Applications

COATINGS RECOMMENDED FOR CUTTINGS TAPS

TiN

TiCN

TiX2

TiH1

CRN

TiAlN

ACE

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

TiH1

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.
aswdfoh
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.
asf
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).
aqwgfaq
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.
awdfw
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.
asdf
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.
AWDERFQ
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.
asdWF
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.
fagsw
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.
saf
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.
wadef
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.
 

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

Drill sizes cutting Taps

ISO Metric coarse thread - DIN 13

M Pitch
[mm]
Maximum
core diam.
(toll. 6H)
[mm]
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

M Pitch
[mm]
Maximum
core diam.
(toll. 6H)
[mm]
Drill size *
[mm]
M Pitch
[mm]
Maximum
core diam.
(toll. 6H)
[mm]
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

EG-M Drill size *
[mm]
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
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

Unified coarse thread - UNC ASME - B1.1

UNC T.P.I. Maximum
core diam.
(class. 3B)
[mm]
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

UNF T.P.I. Maximum
core diam.
(class. 3B)
[mm]
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
       

8-UN thread - ASME B1.1

8-UN T.P.I. Maximum
core diam.
(class. 3B)
[mm]
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
       
       

Whitworth thread - BS 84

BSW T.P.I. Maximum
core diam.
[mm]
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

G T.P.I. Maximum
core diam.
[mm]
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

Rp T.P.I. Maximum
core diam.
[mm]
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
NPT - National pipe thread, taper 1:16 - ANSI B1.20.1
NPTF - Dryseal National pipe thread, taper 1:16 - ANSI B1.20.3

Cylindrical hole, without using a reamer

Diam TPI D1 [mm] t1 [mm] Prefori cilindrici
NPT
NPTF
Rc
(BSPT)
NPT NPTF Rc
(BSPT) 
NPT
NPTF
Rc
(BSPT) 
1/16" 27 28 6,15 6,15 6,2 12 11,9
1/8" 27 28 8,5 8,5 8,2 12 11,9
1/4" 18 19 11 11 11 17,5 17,7
3/8" 18 19 14,5 14,5 14,5 17,6 18,1
1/2" 14 14 17,85 17,8 18 22,9 24
3/4" 14 14 23,2 23 23,5 23 25,3
1" 11 1/2 11    29 29 29,5 27,4 30,6
1 1/4" 11 1/2 11    37,8 37,8 38 28,1 32,9
1 1/2" 11 1/2 11    44 43,8 44 28,4 32,9
2" 11 1/2 11    56 56 55,5 28,4 37,2

Cylindrical holes with use of tapered reamer

Diam TPI D2 [mm] D3 [mm] t1 [mm] Prefori cilindrici ripassati con alesatore conico
NPT
NPTF
Rc
(BSPT)
NPT
NPTF
Rc
(BSPT)
NPT NPTF Rc
(BSPT) 
NPT
NPTF
Rc
(BSPT)
1/16" 27 28 5,95 6,1 6,39 6,41 6,56 12 11,9
1/8" 27 28 8,25 8,1 8,74 8,76 8,57 12 11,9
1/4" 18 19 10,75 10,75 11,36 11,4 11,45 17,5 17,7
3/8" 18 19 14,1 14,25 14,8 14,84 14,95 17,6 18,1
1/2" 14 14 17,5 17,75 18,32 18,33 18,63 22,9 24
3/4" 14 14 22,7 23 23,67 23,68 24,12 23 25,3
1" 11 1/2 11 28,6 29 29,69 29,72 30,29 27,4 30,6
1 1/4" 11 1/2 11 37,3 37,5 38,45 38,48 38,95 28,1 32,9
1 1/2" 11 1/2 11 43,4 43,5 44,52 44,55 44,85 28,4 32,9
2" 11 1/2 11 55,5 55 56,56 56,59 56,66 28,4 37,2

Preparation of tapered blind hole

Preparazione foro cieco conico
Diam TPI D3 [mm] b [mm] t [mm] D4 [mm]
NPT
NPTF
Rc
(BSPT)
NPT NPTF Rc
(BSPT) 
NPT NPTF Rc
(BSPT) 
NPT NPTF Rc
(BSPT) 
NPT NPTF Rc
(BSPT) 
1/16" 27 27 6,39 6,41 6,56 7 8 5,6 10 11 9,5 7,6 7,4 7,6
1/8" 27 27 8,74 8,76 8,57 7 8 5,6 10 11 9,5 10 9,8 9,6
1/4" 18 18 11,36 11,4 11,45 10,2 11,6 8,4 14,5 15,5 14 13,1 12,9 13
3/8" 18 18 14,8 14,84 14,95 10,6 12 8,8 15 16 14,4 16,5 16,3 16,5
1/2" 14 14 18,32 18,33 18,63 13,8 15,6 11,4 19 20,5 19 20,5 20,3 20,6
3/4" 14 14 23,67 23,68 24,12 14,2 16 12,7 20 21,5 20,3 25,8 25,6 26
1" 11 1/2 11 1/2 29,69 29,72 30,29 17 19,2 14,5 24 26 24,3 32,2 32 32,8
1 1/4" 11 1/2 11 1/2 38,45 38,48 38,95 17,5 19,7 16,8 24,5 26,5 26,6 41 40,8 40,2
1 1/2" 11 1/2 11 1/2 44,52 44,55 44,85 17,5 19,7 16,8 24,5 26,5 26,6 47,2 47 47,2
2" 11 1/2 11 1/2 56,56 56,59 56,66 18 20,2 21,1 25 27 30,9 59,2 59 58,7

Drill sizes forming Taps

ISO Metric coarse thread - DIN 13

M 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

MF 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

G 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

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.

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.

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