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How To Measure Fastener Length

At one time or another, all of us (even the pros) mismeasure a fastener.  Not that the guys at the hardware store don't need a chuckle every now and them.  Use this handy chart, courtesy BoltDepot.com, to get the measurement right the first time!

General Fastener Measurement Guidelines

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

Round head machine screw

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

Flat hear machine screw

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.

Measuring Specific Types of Fasteners

Below are a number of common fasteners with a graphic of the proper measurement area.  This is posted strictly for your viewing pleasure, but ALL CONFORM TO THE RULE ABOVE REGARDING GENERAL FASTENER MEASUREMENT.

Hex Bolts

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

Hex bolt

Wood Screws

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

Countersunk (Flat or Oval head) are measured overall.

Flat head and oval head wood screws

Round head screws are measured from under the head.

Round head screw

Machine Screws

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

Countersunk (Flat or Oval head) is measured overall.

Flat and oval head machine screws

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

Pan or round head machine screws

Carriage Bolts

Carriage bolts are measured from directly under the head.

Carriage bolt

Lag Bolts (Lag Screws)

Lag Bolts are measured from under the head.

Lag screw

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.

Flat or oval head countersunk screws

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

Pan, truss head and hex head screws

Socket Products

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

Flat Socket Caps are measured by the overall length.

Flat socket caps

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

Socket head caps and button head caps

Our thanks to BoltDepot, your online source for ALL your fastener needs, for sharing this chart with us!

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