A easy way to describe one type of knurl is the crosshatch pattern you find on allot of the cheaper ratchets for the handle. The part that is knurled on wheel studs is the splined section that creates the interference fit on the wheel stud. It is primarily created by putting enough pressure on round stock to deform the material into the desired shape, but it can also be created by cutting.
Hey Dirt Mine are from a v8 5 lug axle I wouldn't think the I6 4 lug studs would smaller . Are you measuring the knurl or the stud size . Just went out and remeasured thread size is .490 shoulder is .590 and knurl is .615.. Jay
Just bought one for a 74 8" 5 lug rear end, knurl was .545, must be some different sizes out there I need to get some longer ones for front to comply with NHRA rules so that will be one of my next quest