[Yosemite Sam]

In the back of the pto where the bearing is, you will notice that the points on the set screws do not prick into the sides of the bearing.

The point actually goes behind the bearing. In theory, the tighter you tighten the screws the further they would push the bearing into the pto.

This probably doesn't really mean much to you EXCEPT, when you drill through the screws and the drill bit hits the bearing, if you aren't very careful, it will almost always break the drill bit.

I which case, you now not only have a stuck set screw, you also have a broken drill bit that you can't get out.

Also keep in mind that those set screws are HARD, your drill speed should be very slow and keep the hole being drilled full of coolant/cutting fluid.

I personally will spend tons of time extracting the screws and exhaust every effort to remove them rather than drill even one of them out.

One other word of caution, if you take the pto apart and try to drive the bearing out the back side without getting the set screws out of the way, you will break the casting rendering it useless, and expensive to replace.

Good Luck