Bolt patterns are expressed as the number of studs and the diameter of an imaginary circle that passes through the center of the wheel studs.

The diameter can be measured in either inches or millimeters. In the case of a JK Wrangler the diameter is 127mm or 5 inches, so the bolt pattern can be stated as either 5×127 or 5×5″.

Bolt pattern diameter shown in read, as formed by the 5 studs

Actual measurements for hubs with even numbers of wheel studs (4, 6 and 8) is fairly simple. Measure from the center of a stud to the center of the opposing stud. For the studs to be opposing the line of measure between them will pass through the center of the hub (as shown by the read line below).

For hubs with odd numbers of studs, a measurement can only be approximated with out the use of specialized tools such as a bolt pattern gauge. To get a close estimate, measure from a stud center to the center of either one of the opposing studs and multiply by 1.05 for 5 stud hubs or 1.03 for a 7 stud hubs.

Alternately, a reasonable estimate can be achieved (without math) by measuring from the center of a stud to the far side or the opposing stud.

As bolt patterns to most makes and models are readily available on the net, there’s really only a few reasons for making bolt pattern measurements. Nonetheless a wide assortment of tools is available to make the task easier just in case you encounter an odd ball pattern on some cobbled together rig.

The following is a list of the more common bolt pattern gauges tools.