Measuring Fastener Length

This technical information has been supplied by boltdepot.com

General

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

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

  • 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.

Machine_Screw_Length_Pan_Head.gif
Machine_Screw_Length_Flat_Head.gif

Specific Types

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

Hex_Bolt_Length.gif

Wood Screws

Wood screw measurement depends upon the type of screw you are using.
Countersunk (Flat or Oval head) are measured overall.

Wood_Screw_Length_Flat_Head.gif
Wood_Screw_Length_Oval_Head.gif
Wood_Screw_Length_Round_Head.gif

Round head screws are measured from under the head.

Machine Screws

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

Countersunk (Flat or Oval) is measured overall.

Machine_Screw_Length_Flat_Head.gif
Machine_Screw_Length_Oval_Head.gif
Machine_Screw_Length_Pan_Head.gif

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

Machine_Screw_Length_Round_Head.gif

Carriage Bolts

Carriage bolts are measured from directly under the head.

Carriage_Bolt_Length.gif

Lag Bolts (Lag Screws)

Lag Bolts are measured from under the head

Lag_Bolt_Length.gif

Sheet Metal Screws

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

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

Sheet_Metal_Screw_Length_Flat_Head.gif
Sheet_Metal_Screw_Length_Oval_Head.gif

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

Sheet_Metal_Screw_Length_Hex_Head.gif
Sheet_Metal_Screw_Length_Pan_Head.gif

Socket Head Products

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

Flat Socket Caps are measured by the overall length.

Socket_Cap_Length_Flat_Head.gif
Socket_Cap_Length_Socket_Cap_Head.gif

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

Socket_Cap_Length_Socket_Pan_Head.gif