Imperial Machine Screw Size Guide

Bronze Machine Screws

When selecting the right imperial machine screw for your project, it's essential to understand the precise measurements, including thread diameter and head diameters ASME B18.6.3 sets the standard for machine screws, ensuring consistency in manufacturing and application.

Our machine screw size guide provides detailed specifications to help you choose the correct screw for your needs. Whether you're working with our marine grade 316 stainless machine screws or silicon bronze machine screws.

 

MACHINE SCREW HEAD DIAMETERS

Head Diameter
Nominal Size Max. Min.
#2
#4
#5
#6
#7
#8
#9
#10
#12
1/4"
5/16"
3/8"
1/2"		 0.172"
0.225"
0.252"
0.279"
0.305"
0.332"
0.358"
0.385"
0.438"
0.507"
0.635"
0.762"
0.875"		 0.147"
0.195"
0.220"
0.244"
0.268"
0.292"
0.316"
0.340"
0.389"
0.452"
0.568"
0.685"
0.775"
316 Stainless Machine Screws

MACHINE SCREW THREAD DIAMETERS AND THREAD COUNTS

Nominal Size, Threads/lnch & Series Designation Allowance Major Diameter Pitch Diameter
Max Min Max Min Tolerance
0-80
1-64
1-72
2-56
2-64		 UNF
UNC
UNF
UNG
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		 UNG
UNF
UNG
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
UNG
UNF
UNG
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		 UNG
UNF
UNG
UNF
UNG		 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
UNG
UNF
UNG
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		 UNG
UNF
UNG
UNF
UNG		 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"
9/16"-18
5/8"-11
5/8"-18
3/4"-10
3/4"-16		 UNF
UNG
UNF
UNG
UNF		 0.0014"
0.0016"
0.0014"
0.0018"
0.0015"		 0.5611"
0.6234"
0.6236"
0.7482"
0.7485"		 0.5524"
0.6113"
0.6149"
0.7353"
0.7391"		 0.5250"
0.5644"
0.5875"
0.6832"
0.7079"		 0.5205"
0.5589"
0.5828"
0.6773"
0.7029"		 0.0045"
0.0055"
0.0047"
0.0059"
0.0050"
7/8"-9
7/8"-14
1"-8
1"-12
1"-14		 UNG
UNF
UNG
UNF
UNS		 0.0019"
0.0016"
0.0020"
0.0018"
0.0017"		 0.8731"
0.0834"
0.9980"
0.9982"
0.9983"		 0.8592"
0.8631"
0.9830"
0.9868"
0.9880"		 0.8009"
0.8270"
0.9168"
0.9441"
0.9519"		 0.7946"
0.8216"
0.9100"
0.9382"
0.9463"		 0.0063"
0.0054"
0.0068"
0.0059"
0.0056"
1-1/8"-7
1-1/8"-8
1-1/8"-12
1-1/4"-7
1-1/4"-8		 UNG
UN
UNF
UNG
UN		 0.0022"
0.0021"
0.0018"
0.022"
0.0021"		 1.1228"
1.1229"
1.1232"
1.2478"
1.2479"		 1.1064"
1.1079"
1.1118"
1.2314"
1.2329"		 1.0300"
1.0417"
1.0691"
1.1550"
1.1667"		 1.0228"
1.0348"
1.0631"
1.1476"
1.1597"		 0.0072"
0.0069"
0.0060"
0.0074"
0.0070"
1-1/4"-12
1-3/8"-6
1-1/8"-8
1-3/8"-12
1-1/2"-6		 UNF
UNC
UN
UNF
UNC		 0.0018"
0.0024"
0.0022"
0.0019"
0.0024"		 1.2482"
1.3726"
1.3728"
1.3731"
1.4976"		 1.2368"
1.3544"
1.3578"
1.3617"
1.4794"		 1.1941"
1.2643"
1.2916"
1.3190"
1.3893"		 1.1879"
1.2563"
1.2844"
1.3127"
1.3812"		 0.0062"
0.0080"
0.0072"
0.0063"
0.0081"
1-1/2"-8
1-1/2"-12
1-5/8"-8
1-3/4"-5
1-3/4"-8		 UN
UNC
UN
UNC
UN		 0.0022"
0.0019"
0.0022"
0.0027"
0.0023"		 1.4978"
1.4981"
1.6228"
1.7473"
1.7477"		 1.4828"
1.4867"
1.6087"
1.7268"
1.7327"		 1.4166"
1.4440"
1.5416"
1.6174"
1.6665"		 1.4093"
1.4376"
1.5342"
1.6085"
1.6590"		 0.0073"
0.0064"
0.0074"
0.0089"
0.0075"
Back to blog