Good point and yes the Japanese are likely deeper. Again, I don't have a Burman sprocket to compare, but just a quick comparison to a Norton shows the Japanese splines .5mm deeper. In this case the splines (on the Norton) are just over 7mm wider, but some of the extra width is due to the shoulder that the output seal runs on which the Burman sprocket doesn't have. (Japanese shaft is about 6.75mm smaller in diameter). Not that any of this matters in the grand scheme of things...just find it interesting.
The splines in Martyn's photo look odd to me. Probably just the photo, but the groove shown by the top arrow doesn't appear to be in the spline indicated by the lower arrow. In any event, when welding up the splines that groove or whatever it is ( perhaps from a washer fretting away) looks like it should be filled in to maximize the load bearing area, making sure the threads don't go any deeper than necessary.
Martyn, if your new sprocket has good splines, but worn teeth, you could always do as Robert does and graft new teeth on it. He is our resident orthodontist.
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