Measuring bolt patterns is a critical part of ordering wheels.  The correct terminology for referencing bolt patterns is to

say the number of lug holes/studs on measurement, such as : 5 on 4.5 or 6 on 135mm.

The distance that you are measuring is the diameter of a circle intersecting the center of each lug hole/stud.

Measuring Bolt Patterns

All Even-numbered lugs can be determined by simply measuring the distance  from the center of one lug hole/stud to the center of the opposite lug hole/stud across the centerbore.

This applies to 4, 6, 8 or 10 lug vehicles and wheels
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Many times, aftermarket wheels are drilled with two bolt patterns  on one wheel.  This allows us to fit more vehicles with less inventory.  You will typically see two 4-lug, 5-lug or 6-lug bolt patterns on one wheel.  There are rare cases where you will notice a 4-lug and 5-lug combination on one wheel.  This is achieved by using one lug hole for both bolt patterns as illustrated in the diagram above:

Notice the dual colored lug hole is used for the 4-lug and 5-lug application.  An example would be a 4 x 100 and 5 x 100 bolt pattern.

All Odd-numbered lugs can be approximately determined by measuring the distance  from the center of one lug hole/stud to the outside edge of the opposite lug hole/stud across the centerbore.

This applies to 3, 5 or 7 lug vehicles and wheels.