For what it's worth:
When the "American Society of Agricultural Engineers" recognized that the
increasing horsepower of tractors was stressing the 1 3/8" 6 spline 540 RPM
power-take-off shaft of the tractors being produced, they elected a new
standard with gearing of 1000 RPM which effected a lowering of the torque load
to about half that of the old standard. At this time they also changed the
spline configuration from 6 splines to 21 splines. I feel sure that they did
NOT change to a spline count which had LESS
ultimate strength than to original.
Tony
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