New article on my site, take a look: http://victorylibrary.com/mopar/axle-spline.htm

So isn't root diameter a better/more accurate indicator then spline count, and harder to know, and why the focus is usually on spline counts?
But then why is it to anyone's advantage to cut more splines, if strength is only marginally increased if root diameter is almost the same, ie trans inputs, pinion yokes, etc?

The point is that they don't just cut more splines, the diameter is always increased proportionate to the spline count, and the carrier's spline count must (duh) also match.
With the same spline contour, a 40 spline axle is 33% thicker than a 30 spline, etc.

thanks for putting up another great article !

The contour of axle splines, at least on the stuff were talking about, are pretty consistent between manufacturers. Mark Williams uses a little different shape, but for the most part, a 40 spline axle is pretty much the same size across the board. Larger diameter = more splines. When discussing strength and resistance to twisting and/or breaking, other things have to be considered. Material and heat treat methods, machining methods (radii vs. sharp corners, etc.), solid vs. gun drilled and many other details. They aren't all made with the same stuff and the same way.

Mark Williams splines are rolled in , most others are cut. A Mark Williams axle will fit in about any 40 spline spool, but the opposite is not true. Meaning most other axles won't fit MW spools

MW is top notch.
I realize it's a less costly process to cut splines & it also surprises me that others wouldn't have a rolled spline axles, which are stronger.

Rolled splines are better, but the machinery to do it is not cheap. Seldom do you see broken 40 spline axles and most companies warranty their 40 splines against breakage anyway. So if you aren't seeing many broken, why change.

Moser and Dutchman splines are milled.

Mark Williams, as well as Strange cut their splines on a hob.

Admittedly I have not looked at any Strange axles recently. If they are "hobbing" axle splines now, are they doing them involute or straight sided. Have they gone to the 45* angle, or are they still 30*

Strange has always used involute (curved profile) hobbed splines.

Pressure angle depends on the application. For example, OEM and replacement Ford and GM shafts have 45 degree pressure angle splines, regardless of the source.

Mark Williams is the only manufacturer that uses a 45 degree pressure angle for 35 and 40 spline axles, however. Every other company uses 30 degree in that application.