Tech Info

Glossary of terms

Annealing Heating and slow cooling to remove stresses, make steel softer, refine the structure, or change its ductility.

Carburizing Adding carbon to the surface of iron-based alloys by heating the metal below its melting point in contact with carbon-rich solids, liquids or gases.

Cyanide Hardening A method of case hardening which brings the metal surface in contact with the molten cyanide salt followed by a quenching.

Decarburization Removal of carbon from the surface of steel. This can occur through normal oxidizing action or as the result of heat treatment.

Drawing (Tempering) Reheating after hardening , held at a specific temperature and then quenched. This reduces hardening and increases toughness.

Hydrogen Embrittlement A condition where the surface finishing of metal (plating) results in a brittle outer case due to immersion in acid. Baking immediately following the plating process removes this brittle surface condition.

Nitriding A hardening process which adds nitrogen to a metal surface through contact with ammonia gas. Produces surface hardness (case) without quenching.

Precipitation Hardening A hardening process where certain metals are held at elevated temperature without quenching (age hardening).

Quenching Rapid cooling of steel by immersion in oil or water to fix its structure in a hardened state.

Sphereoidizing (anneal) Any process of heating and cooling steel that produces a rounded or globular form of carbide. This softens the metal, improving ductility.

Stress Relieve A low temperature heat treatment which removes stresses caused by cold working.

Thread series

Coarse Thread Series Applications

The coarse thread series (UNC/UNRC) is generally used for the bulk production of screws, bolts, and nuts. It is commonly used in relatively low strength materials such as cast iron, aluminum, magnesium, brass, bronze, and plastic because the coarse series threads provide more resistance to internal thread stripping than the fine or extra-fine series. Coarse series threads are advantageous where rapid assembly or disassembly is required, or if corrosion or damage from nicks due to handling or use is likely.

Fine Thread Series Applications

The fine thread series (UNF/UNRF) is commonly used for bolts and nuts in high strength applications. This series has less thread depth and a larger minor diameter than coarse series threads. Consequently, thinner walls are permitted for internal threads and more strength is available to external threads than for coarse series threads of the same nominal size.

8-Thread Series

The 8-thread series (8UN) is a uniform-pitch series for large diameters or as a compromise between coarse and fine thread series. Although originally intended for high-pressure-joint bolts and nuts, it is now widely used as a substitute for the coarse thread series for diameters larger than 1 inch.

12-Thread Series

The 12-thread series (12UN) is a uniform-pitch series for large diameters requiring threads of medium-fine pitch. Although originally intended for boiler practice, it is now used as a continuation of the fine thread series for diameters larger than 1-1/2 inch.

 

Thread Identification Chart (Metric) 
Coarse Fine 
Diameter Pitch Diameter Pitch 
1st Choice 2nd Choice 
1st Choice 2nd Choice 1st Choice 2nd Choice 
M2 
0.4



M2.5 
0.45



M3 
0.5



M4 
0.7



M5 
0.8



M6 
1




M7 1



M8 
1.25M8 
1
M10 
1.5M10 
1.251
M12 
1.75M12 
1.251.5

M14 2
M14 1.5
M16 
2M16 
1.5

M18 2.5
M18 1.52
M20 
2.5M20 
1.52

M22 2.5
M22 1.52
M24 
3M24 
2

M27 3
M27 2
M30 
3.5M30 
2

M33 3.5



M36 
4




M39 4



M42 
4.5




M45 4.5



M48 
5




M52 5



M56 
5.5



Thread Identification Chart (Unified Standard) 
Diameter UNC Thread UNF Thread Diameter UNC Thread UNF Thread 
No.0 - 809/16" 1218
No.1 64725/8" 1118
No.2 56643/4" 1016
No.3 48567/8" 914
No.4 40481" 814(12)* 
No.5 40441-1/8" 712
No.6 32401-1/4" 712
No.8 32361-3/8" 612
No.10 24321-1/2" 612
No.12 24281-3/4" 5- 
1/4" 20282" 4-1/2"- 
5/16" 18242-1/4" 4-1/2"- 
3/8" 16242-1/2" 4- 
7/16" 14202-3/4" 4- 
1/2" 13203" 4- 
Thread Identification Chart (British) 
Diameter BSW Thread BSF Thread Diameter BSW Thread BSF Thread 
1/4" 20267/8" 911
5/16" 18221" 810
3/8" 16201-1/8" 79
7/16" 14181-1/4" 79
1/2" 12161-3/8" - 8
5/8" 11141-1/2" 68
3/4" 10121-5/8" - 8
BSW - British Standard Whitworth     BSF - British Standard Fine 
Imperial/Decimal/Metric Chart For Small Diameters 
Gauge or Dia. Decimal (in) Decimal (mm) Gauge or Dia. Decimal (in) Decimal (mm) 
No.0000 0.0210.53No.4 0.1122.845
No.000 0.0340.86No.5 0.1253.175
No.00 0.0471.19No.6 0.1383.505
No.0 0.061.524No.8 0.1644.166
No.1 0.0731.854No.10 0.194.826
No.2 0.0862.184No.12 0.2165.484
No.3 0.0992.515No.14 


Steels generally used for metric screws, bolts and studs
Property Class SizeMaterials per DIN 1)Materials per ANSI 1)
3.6to M39QSt 36-21006
4.6USt 38-21010

UQSt 36-2

UQSt 38-2
4.8to M16QSt 36-21006
QSt 38-21010
5.6to M39Cq 221022
5.8to M39Cq 221022
Cq 351035
8.8to M1222B210B22
28B210B28
Cq 351035 (1038)
to M2235B210B35
Cq 351035 (1038)
Cq 451045
46 Cr 1
over M2434 Cr 45132
to M3937 Cr 45135

46 Cr2
10.9to M635B210B35
Cq 351035
over M634 Cr 45132
to M1841 Cr 45140
to M3941 Cr 45135
34 CrMo 44137
42 CrMo 44140
12.9to M1834 CrMo44137
37 Cr 45135
41 Cr 45140
to M2442CrMo 44140
to M3934 CrNiMo 64340
ISO Tolerances
Nominal DimensionTolerance Zone in mm (External Measurements)
overtom6h6h8h10h11h13h14h15h16
010.00200000


0.008-0.006-0.014-0.04-0.06-0.14
130.00200000000
0.008-0.006-0.014-0.04-0.06-0.14-0.25-0.4-0.6
360.00400000000
0.012-0.008-0.018-0.048-0.075-0.18-0.3-0.48-0.75
6100.00600000000
0.015-0.009-0.022-0.058-0.09-0.22-0.36-0.58-0.9
10180.00700000000
0.018-0.011-0.027-0.07-0.11-0.27-0.43-0.7-1.1
18300.00800000000
0.021-0.03-0.033-0.084-0.13-0.33-0.52-0.84-1.3
3050




0000
-0.39-0.62-1-1.6
5080




0000
-0.46-0.74-1.2-1.9
80120




0000
-0.54-0.87-1.4-2.2

 

Nominal DimensionTolerance Zone in mm (External Measurements)
overtojs14js15js16js17
13+0.125+0.2+0.3+0.5
----
36+0.15+0.24+0.375+0.6
----
610+0.18+0.29+0.45+0.75
----
1018+0.215+0.35+0.55+0.9
----
1830+0.26+0.42+0.65+1.05
----
3050+0.31+0.5+0.8+1.25
----
5080+0.37+0.6+0.95+1.5
----
80120+0.435+0.7+1.1+1.75
----
120180+0.5+0.8+1.25+2
----
180250+0.575+0.925+1.45+2.3
----
250315+0.65+1.05+1.6+2.6
----
315400+0.7+1.15+1.8+2.85
----
400500+0.775+1.25+2+3.15
----
Nominal DimensionTolerance Zone in mm (Internal Measurements)
overtoH7H8H9H11H13H14
010.010.0140.0250.060.14
00000
130.010.0140.0250.060.140.25
000000
360.0120.0180.030.0750.180.3
000000
6100.0150.0220.0360.090.220.36
000000
10180.0180.0270.0430.110.270.43
000000
18300.0210.0330.0520.130.330.52
000000
3050



0.390.62
00
5080



0.460.74
00
80120



0.540.87
00