How to Measure the Socket Wrench Size for a Bolt

Steve Sloane

Socket wrench sets contain different sized enclosed socket heads that are used to tighten or remove nuts, bolts and bolt-shaped screw heads. The enclosed socket head creates more leverage as it completely surrounds the nut or bolt head.

Use a bolt-sizing gauge to determine the correct socket head size.

Most socket heads have either 6 or 12 points to grip the bolt and decrease any possibility of slippage while being used. Determining the size of socket head to match the bolt is a simple, quick process.


If no bolt-sizing gauge is available, choose a socket head from the socket set that looks like the correct size to fit the bolt head. Attempt to fit this onto the bolt head, or try other socket heads until you get a good fit. Chose the socket head that slips easily onto the bolt and provides the least amount of wiggle room.

  1. Insert the shank of the bolt into the holes in a bolt-sizing gauge. The correct size hole will allow little wiggle room for the bolt's shank.

  2. Locate the printed bolt size to the side of the correct hole on the gauge (for example, 1/2, 3/4 or in mm for metric bolts).

  3. Locate the socket head in the socket set that has this size printed on its side. Position this socket onto the bolt head to ensure it is the correct size. The socket head should fit snugly and easily around the bolt head, providing little to no wiggle room. If it is the correct size, snap the socket head onto the socket arm so it is ready for use.