How do you determine which size lugs are needed to mount the wheels on a rear axle? The length is easy to determine, the problem is the knurled portion of the stud. Summit, for example, has 1/2 inch lugs with a .594 knurl, a .615 knurl and a .625 knurl. Obviously, the knurled area must be larger than the hole in the axle flange. The question is how to determine how much larger does it need to be to properly fit.