Very curious...........

TOH

And while TOH, is correct that you can accurately measure the PTO's splined shaft with a dial-caliper, I'll bettcha yer nekkid eyeball is plenty accurate enuff. You doubt? Just hold yer thumb and finger up for an airgap of about 1-in, gottitt? Now widen-out yer airgap for an inaccurate 1-1/2" airgap.

Now that you've calibrated yer eyeball, go out and estimate yer 1" airgap and compare with yer PTO splines. Close? ya gotta 1-1/8 spline. Way too small? try yer 1-1/2" airgap and compare with yer PTO splines. Overfits? ya gotta 1-3/8 spline. See how precisionally accurate yer eyeball is? Simple, eh?..... ....Dell the eyeballer

The OEM pto shaft was 6 spline 1 1/8" The updated pto shaft is 6 spline 1 3/8"

He can change the shaft ( 15 minute / 4 bolt/ 100$ job ).

or

He can get a 1 1/8 fem to 1 3/8 male ORC

or

He can get the stamped insert to bushing his 1 1/8 up to 1 3/8

or

he can get a stub expander that slides over the 1 1/8 in much the same way the bushing does.. however it is longer and makes the 1 1/8 come up tot he same length, shoulder and width as a modern 1 3/8 shaft stub.

or

He can get a 1 1/8 yoke to fit his mower.

I vote for the orc or a new shaft and the orc.

Using an orc is not as critical on a finish mower.. but they never hurt on anything with any rotary inertia.

For finsih mowing.. the bushing and stub extender would work fine too.. It's rotary mowing and post hole augering that will eat that little bushing up ( anything with high or shock loads.. )

Soundguy

TOH