On a 70's era 21" Snapper push mower, the end of the shaft is larger
than the rest of the shaft. I don't have it in front of me to measure
but the last maybe 1/4 inch of the shaft is approximately the size of
a quarter, flat on two sides. There are also washers with center holes
that are shaped approximately like that end of the shaft - the hole
flat on the sides, though a bit larger than the shaft end.

The center hole in the blade is round and slightly larger than this
shaft end. How is that blade actually supposed to be mounted? I know
there are clutch washers involved - is the hole in the blade supposed
to be around that larger end or is it supposed to be further up the
shaft and centered basically by eye and held in place by the friction
of the washers clamping down on it?

Thanks.