Ester,
Lets assume you have a 5 module spline.
25.4 divided by 5 equals 5.08 diametral pitch.
I would think the addendum would be 40 percent
times the module ie. double stubbed form.
Stub gear is 80 percent times the module.
Assume the material UTS is 100,000psi
Spline interface b length is .75 inches.
Assume 24 teeth. (Y factor .5 guess)
Did not layout the teeth.
Then max load would be 24 times sbY/diametral pitch
24 times (.50 x 100000) times .75 times .5 / 5.08
equals 88583 pounds.
5 module with 24 teeth is 120mm pitch diameter
or 60mm radius or .19685 feet radius.
.19685 times 88583 yields 17438 ft-lbs (foot pounds)
torque or 23643 Newton Meters torque.
Will let you check the math!