Customer:"Hello? I'd like to buy an axleshaft for my Ford 9-inch rear axle." Salesperson:"No problem. Do you know what length, spline count, and wheel-bolt pattern you need?" Customer:"I really don't.

The Chevy 12-bolt axle shaft (left) is tapered; the Ford 9-inch shaft is the same diameter throughout its length, except for the short section just after the spline end. This makes it easy to narrow ...