Machine Screw Sizes & Head Types

Use this guide to help you find the screw size number or fractional size. Then select the head type that meets your needs.

12/6/19 - Zoro Staff

Background

What is a machine screw?

A machine screw is like a small-diameter bolt or hex head cap screw, but is usually driven with a screwdriver instead of a wrench. It features a straight, untampered shank and blunt end. External machine thread runs the entire length of the shank.

How Are Machine Screws Used?

Most commonly used to fasten metal to metal, a machine screw is designed to be inserted into a pre-threaded hole or mated with a nut (in which case it would be called a stove bolt).

Because application thread sizes vary, it is important to select the right machine screw to meet your specific requirements.

Find Machine Screw Size Number or Fractional Size

Use the conversion charts below to find screw size number or fractional size.

Screw Size Conversion Chart

Screw Size

Fractions

Decimals

Millimeter

 
#1 1/16" 0.0625"

1.58750

Shop #1 Screws
#2 5/64"

0.078125"

1.98437 Shop #2 Screws
#3 3/32" 0.09375" 2.38125 Shop #3 Screws
#4 7/64" 0.109375" 2.77812 Shop #4 Screws
#5 1/8" 0.125"

3.17500

Shop #5 Screws
#6 9/64"

0.140625"

3.57187 Shop #6 Screws
#8 5/32" 0.15625" 3.96875 Shop #8 Screws
#9 11/64"

0.171875"

4.36562  
#10 3/16" 0.1875" 4.76250 Shop #10 Screws
#11 13/64" 0.203125" 5.15937  
#12 7/32" 0.21875" 5.55625 Shop #12 Screws
#13 15/64" 0.234375" 5.95312  
#14 1/4" 0.250"

6.35000

 

#16

17/64"

0.265625"

6.74687

 
#18 19/64" 0.296875" 7.54062  
#20 5/16"

0.3125"

7.93750

 
#24 3/8" 0.375" 9.52500  

Standard Threads

UNC UNF  
1/4 x 20" 1/4 x 28 Shop 1/4 x 20" Screws
5/16 x 18" 5/16 x 24 Shop 5/16 x 18" Screws
3/8 x 16" 3/8 x 24 Shop 3/8 x 16" Screws
7/16 x 14"

7/16 x 20

 
1/2 x 13" 1/2 x 20 Shop 1/2 x 13" Screws
5/8 x 11"

5/8 x 18

 
3/4 x 10"

3/4 x 16

 
7/8 x 9"

7/8 x 14

 
1 x 8"

1 x 14

 

Select a Head Type

Flat

Pan

Round

Oval

Truss

Hex

Button

Cheese

Fillister

Binding

Tamper-Resistant Machine Screws

Security fastners, as the name indicates, provide an added level of security by their drive design — preventing removal with ordinary screwdrivers.

Screws are available in sheet metal and machine threads.

Torx

One-Way

Spanner

Tri-Groove

Hex

Still Need Help?

If you are still having trouble choosing a machine screw, contact our Customer Service team at askzoro@zoro.com or call 855-289-9676.

Product Compliance and Suitability

The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.