Machine Screws

Machine screws are standardized in a variety of sizes and head styles but are mainly 3/8 or less with a few exceptions for larger sizes. Pan head and round head are the most basic where the head of the screw is on top of the work surface.

Flat heads and oval heads are used when the head is countersunk into the work surface. Fillister heads are used in counter bored holes.

Machine screws are also available with hex heads. Machine screws are available in low carbon steel and non corrive material like stainless steel, silicon bronze or aluminum.

Following is a list of standard US Thread sizes for Machine Screws. Please check under the head styles listed for the type you wish to see.

Nominal Size & Threads/inch & Series Designation		Allowance	Major Diameter		Pitch Diameter
Nominal Size & Threads/inch & Series Designation		Allowance	Max	Min	Max	Min	Tolerance
0-80 1-64 1-72 2-56 2-64	UNF UNC UNF UNC UNF	0.0005 0.0006 0.0006 0.0006 0.0006	0.0595 0.0724 0.0724 0.0854 0.0854	0.0563 0.0686 0.0689 0.0813 0.0816	0.0514 0.0623 0.0634 0.0738 0.0753	0.0496 0.0603 0.0615 0.0717 0.0733	0.0018 0.0020 0.0019 0.0021 0.0020
3-48 3-56 4-40 4-48 5-40	UNC UNF UNC UNF UNC	0.0007 0.0007 0.0008 0.0007 0.0008	0.0938 0.0983 0.1112 0.1113 0.1242	0.0938 0.0942 0.1061 0.1068 0.1191	0.0848 0.0867 0.0950 0.0978 0.1080	0.0825 0.0845 0.0925 0.0954 0.1054	0.0023 0.0022 0.0025 0.0024 0.0026
5-44 6-32 6-40 8-32 8-36	UNF UNC UNF UNC UNF	0.0007 0.0008 0.0008 0.0009 0.0008	0.1243 0.1372 0.1372 0.1631 0.1632	0.1195 0.1312 0.1321 0.1571 0.1577	0.1095 0.1169 0.1210 0.1428 0.1452	0.1070 0.1141 0.1184 0.1399 0.1424	0.0025 0.0028 0.0026 0.0029 0.0028
10-24 10-32 12-24 12-28 1/4-20	UNF UNC UNF UNC UNF	0.0010 0.0009 0.0010 0.0010 0.0011	0.1890 0.1891 0.2150 0.2150 0.2489	0.1818 0.1831 0.2078 0.2085 0.2408	0.1619 0.1688 0.1879 0.1918 0.2164	0.1586 0.1658 0.1845 0.1886 0.2127	0.0033 0.0030 0.0034 0.0032 0.0037
1/4-28 5/16-18 5/16-24 3/8-16 3/8-24	UNF UNC UNF UNC UNF	0.0010 0.0012 0.0011 0.0013 0.0011	0.2490 0.3113 0.3114 0.3737 0.3739	0.2425 0.3026 0.3042 0.3643 0.3667	0.2258 0.2752 0.2843 0.3331 0.3468	0.2225 0.2712 0.2806 0.3287 0.3430	0.0033 0.0040 0.0037 0.0044 0.0038
7/16-14 7/16-20 1/2-13 1/2-20 9/16-12	UNF UNC UNF UNC UNF	0.0014 0.0013 0.0015 0.0013 0.0016	0.4361 0.4362 0.4985 0.4987 0.5609	0.4258 0.4281 0.4876 0.4906 0.5495	0.3897 0.4037 0.4485 0.4662 0.5068	0.3850 0.3995 0.4435 0.4619 0.5016	0.0047 0.0042 0.0050 0.0043 0.0052

Machine Screws Length Tolerances

Nominal Screw Size	O thru l2	1/4 thru 3/4
Nominal Screw Length	Tolerance on Length
Up to 1/2 in., Incl. Over 1/2 to 1 in., Incl. Over 1 to 2 in., Incl. Over 2 in.	-0.02 -0.03 -0.06 -0.09	-0.03 -0.03 -0.06 -0.09

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