Besides feeling the disc on the sides, you can take a round rod,,shaft,socket extension,,ect,,
something round that will fit into the pilot bearing slightly loose,,then see how close to the splines it is all the way around as you gently roll it in a circle trying to touch the center splines on the disc. If the shaft touches the splines,,,, the shaft needs to be bigger.(a little tighter in the bearing) The shaft needs to be loose enough to wiggle around and measure equal distance around the inner circumference of the splines on the disc.
And now that I have you completely confused..........................
I've done this lots of times with never a miss.