How to measure a screw/bolt

Fastener length is measured from where the material surface is assumed to be, to the end of the fastener.

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For fasteners where the head usually sits above the surface, the measurement is from directly under the head to the end of the fastener.

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For fasteners that are designed to be countersunk, the measurement is made from the point on the head where the surface of the material is, to the end of the fastener.


Carriage Bolts

Carriage bolts are measured from directly under the head.

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Eye Bolts

Eye Bolts are measured from under the eye.

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Hanger Bolts

Hanger bolt length is measured from end to end.

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Hex Bolts

Hex bolts are measured from under the head to the tip of the bolt.

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Lag Bolts (Lag Screws)

Lag Bolts are measured from under the head.

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Machine Screws

Machine screw measurement depends on the style of head it has.

  • Countersunk (Flat or Oval head) is measured overall.

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  • Pan Head or Round Head screws are measured from under the head.

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Sex Bolts

Sex bolt length is measured from under the head.

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Sheet Metal Screws

Sheet metal screw measurement depends upon the type of screw you are using.

  • Countersunk screws (Flat or Oval head) are measured by overall length.

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  • Pan Head, Truss Head, and Hex Head screws are measured from under the head.

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Shoulder Bolts

Shoulder bolt length is measured as the length of the shoulder.

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Socket Products

Socket screw measurement depends upon the type of screw you are using.

  • Flat Socket Caps are measured by the overall length.

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  • Socket Head Caps and Button Head Caps are measured from under the head.

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Wood Screws

Wood screw measurement depends upon the type of screw you are using.

  • Countersunk (Flat or Oval head) are measured overall.

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  • Round head screws are measured from under the head.

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