Y'all were so helpful in my other thread that I figured I'd come back to ask another silly question! 
I finally got the ol' rotary cutter at my barn working -- the PTO shaft was bent/stuck, so had to have it cut down, but by golly it works! The blades cut nicely (granted, we're not going for baseball diamond quality grass here, but they do they job), and I seem to be getting the hang of cutting. It's actually quite satisfying to whack down 3 foot high weeds and actually be able to see the fenceline by the time I'm done.
I had just about finished up cutting one of the paddocks the other day when I noticed that the grass I had just driven through hadn't been cut. The PTO was turning, but the blades weren't making that thwack-thwack-thwack noise. I turn off the PTO and the tractor, check out the deck and notice that the shear bolt is gone, the washer and nut sitting nicely on top of the deck next to the gearbox.
So, the bolt did its job. However, this is an ancient International rotary cutter, the paint has worn off so much that I don't know what model it is (I'm 90% sure it was bought in the 70s-80s, maybe 90s), the PTO shaft has no markings, and I have no idea what size shear bolt the PTO shaft takes.
What I do know:
1) From my research, a grade 2 shear bolt is recommended.
2) I measured the diameter of the PTO shaft where the bolt goes in, and it appears to be around 4.5 - 5 inches. The hole itself is about 1/2" wide.
What I don't know, and need some advice on: are shear bolts for PTO shafts a standard size? A quick search shows that the nearby Tractor Supply has these guys, which look about right, but I wanted to check with the experts first.
P.S. Also... anyone know a good place to buy a new PTO shaft cover? The tractor place had to destroy the old one.
I finally got the ol' rotary cutter at my barn working -- the PTO shaft was bent/stuck, so had to have it cut down, but by golly it works! The blades cut nicely (granted, we're not going for baseball diamond quality grass here, but they do they job), and I seem to be getting the hang of cutting. It's actually quite satisfying to whack down 3 foot high weeds and actually be able to see the fenceline by the time I'm done.
I had just about finished up cutting one of the paddocks the other day when I noticed that the grass I had just driven through hadn't been cut. The PTO was turning, but the blades weren't making that thwack-thwack-thwack noise. I turn off the PTO and the tractor, check out the deck and notice that the shear bolt is gone, the washer and nut sitting nicely on top of the deck next to the gearbox.
So, the bolt did its job. However, this is an ancient International rotary cutter, the paint has worn off so much that I don't know what model it is (I'm 90% sure it was bought in the 70s-80s, maybe 90s), the PTO shaft has no markings, and I have no idea what size shear bolt the PTO shaft takes.
What I do know:
1) From my research, a grade 2 shear bolt is recommended.
2) I measured the diameter of the PTO shaft where the bolt goes in, and it appears to be around 4.5 - 5 inches. The hole itself is about 1/2" wide.
What I don't know, and need some advice on: are shear bolts for PTO shafts a standard size? A quick search shows that the nearby Tractor Supply has these guys, which look about right, but I wanted to check with the experts first.
P.S. Also... anyone know a good place to buy a new PTO shaft cover? The tractor place had to destroy the old one.