Machine Screw Thread Dimensions & Specifications

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2A External Threads For Machine Screws And SEMS (ASME B 1.1 (2008))

Nominal Size & Threads per Inch

 Series Designation
 Allowance
 Major Diameter Pitch Diameter Stress Area, in2
 Tensile Strength, a lb., min. (STEEL screws only)
Max  Min Max Min  Tolerance
0-80 0.060 UNF .0005 .0595 .0563 .0514 .0496 .001762 0.00180 -
1-64 0.073 UNC .0006 .0724 .0686 .0623 .0603 .001970 0.00263 -
1-72 0.073 UNF .0006 .0724 .0689 .0634 .0615 .001899 0.00278 -
2-56 0.086 UNC .0006 .0854 .0813 .0738 .0717 .002127 0.00370 -
2-64 0.086 UNF .0006 .0854 .0816 .0753  .0733 .002040  0.00394 -
3-48 0.099 UNC .0007 .0983

.0938

 .0848  .0825  .002302  0.00487 -
3-56 0.099 UNF .0007 .0983  .0942 .0867  .0845  .002191  0.00523 -
4-40 0.112 UNC .0008 .1112  .1061  .0950  .0925  .002507  0.00604  360
4-48 0.112 UNF .0007 .1113  .1068  .0978  .0954  .002361  0.00661 396
5-40 0.125 UNC .0008 .1242 .1191  .1080  .1054  .002562  0.00796  470
5-44 0.125 UNF .0007 .1243 .1195  .1095   .1070  .002484  0.00830 498
6-32 0.138 UNC .0008 .1372 .1312  .1169  .1141  .002820  0.00909  550
6-40 0.138 UNF .0008 .1372 .1321  .1210 .1184 .002614  0.01015  609
8-32 0.164 UNC .0009 .1631 .1571  .1428  .1399  .002916  0.0140  850
8-36 0.164 UNF .0008 .1632 .1577  .1452  .1424  .002804  0.01474  884
10-24 0.190 UNC .0010 .1890 .1818   .1619  .1586  .003319  0.0175 1050 
10-32 0.190 UNF .0009 .1891 .1831  .1688  .1658  .003004  0.0200 1200
12-24 0.216 UNC .0010 .2150 .2078  .1879  .1845  .003400  0.0242 1450
12-28 0.216 UNF .0010 .2150 .2085  .1918  .1886  .003224  0.0258 1548
1/4-20 0.250 UNC .0011 .2489 .2408  .2164  .2127  .003731  0.0318 1900
1/4-28 0.250 UNF .0010 .2490 .2425  .2258  .2225  .003322 0.0364 2200
5/16-18 0.3125 UNC .0012 .3113 .3026  .2752 .2712  .004041  0.0524 3150
5/16-24 0.3125 UNF .0011 .3114 .3042  .2843  .2806  .003660  0.0580 3480
3/8-16 0.375 UNC .0013 .3737 .3643  .3331  .3287  .004363  0.0775 4650
3/8-24 0.375 UNF .0011 .3739 .3667  .3468  .3430  .003804  0.0878 5268
1/2-13 0.500 UNC .0015 .4985 .4876  .4485  .4435  .004965  0.1419 8500
1/2-20 0.500 UNF .0013 .4987 .4906  .4662  .4619  .004288  0.1599 9594
 
Tolerance on Length Nominal Screw Size Nominal Screw Length
Up to 1/2 in., incl. Over 1/2 to 1 in., incl. Over 1 to 2 in., incl. Over 2 in.
0 thru 12 -0.02 -0.03 -0.06 -0.09
1/4 thru 3/4 -0.03 -0.03 -0.06 -0.09



*Tensile strength values are supported 60,000 psi and apply to carbon steel screws and SEMS solely. Hex and Hex Washer Head Machine Screws of enough length is also wedge tensile tested. Different head designs is also axial tensile tested.


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Mechanical & Performance Requirements
Description A straight shank fastener with external threads designed to travel through a hole or nut that's pre-tapped to make a mating thread for the screw.

Applications/
Advantages


 Steel Stainless Aluminum

The most common and most famous variety of steel machine screws is Steel Zinc.

In electronic applications, Steel Zinc yellow screws are common. Black and Black Oxide screws from Steel Zinc are used to blend in with black parts.

 In food processing machinery and cooling devices, 18-8 Stainless Steel machine screws are used in applications requiring general atmospheric corrosion resistance. In resisting any elevation in application operating temperature when retaining its strength, stainless is also superior to steel.

316 Stainless Steel has superior 18-8 corrosion resistance and is superior at elevated temperatures to preserve its strength.

In applications where greater tensile strength is needed, such as control mechanisms or valves under high stress, 410 Stainless Steel is recommended. 410 is not as resistant to corrosion as 18-8 or 316 stainless

 Aluminum machine screws can be a less costly alternative to stainless screws in some applications because of their corrosion resistance and high conductivity rate. To reduce the risk of galvanic corrosion, aluminum machine screws should be fastened with aluminum nuts.
Material  AISI 1006 - 1022 or equivalent steel.  SAE 18-8 stainless steel

316 stainless steel

 410 stainless steel 2024-T4 alloy
Hardness

Rockwell B70 - B100.

 Rockwell B85 - B95 (approximate)* Rockwell B85 - B95 (approximate)* Rockwell C34 (approximate) -

Tensile Strength


60,000 psi. minimum.

  80,000 psi. minimum (100,000 psi after cold working)*  


85,000 - 140,000 psi.


180,000 psi.

  


62,000 psi. minimum

  
     Steel machine screws that are smaller than #4 in nominal diameter are not subject to tensile inspection. Machine screws No. 4 and No. 5 that are shorter than 1/2” are not subject to tensile testing. Tensile testing is not conducted on steel machine screws of diameter 6 to 1/2" inclusive, which are shorter than either 1/2" or 3D (where D is the nominal screw size in inches). 

Such steel machine screws of the size to be measured must comply with the specifications for tensile loads set out above.
Tensile strength values for stainless screws are given only as approximations; there is no single specification for stainless machine screw performance requirements.

  

Plating

  - Stainless machine screws are typically delivered plain or finished in black oxide. Normally, Aluminum machine screws are supplied without any extra finish.  

 *Only for stainless machine screws, hardness and tensile strength requirements are provided as guides. For stainless machine screws, there is currently no national standard for these performance specifications.