Flail mower shear bolt — 12.9?

[Tinhack]

I’m relatively new to tractors and an absolute novice when it comes to PTO shafts…

Is there such thing as a “solid” PTO shaft? (I.e. a U-joint on each end but with no provision for a shear bolt/slip clutch anywhere along its length…)

Yes. Mine doesn't have any provision for a shear bolt or clutch. The "slip" is built into the belts.

 

[Tinhack]

I tend to take into account “worst case scenarios“… implement gearbox failure, PTO U-joint failure etc… so I’m gonna start with a grade 2 bolt and work from there if necessary…

If you go that route, make sure your PTO shaft has a provision that lets it spin without coming off the splined shafts. That would turn into a real destructive mess with a shaft flailing around the output shaft of the tractor. There's been occurrences like this that took out the rear housing of the tractor--Very expensive repair.

Added: Another safety device is the PTO Shield. Make sure your shield chains are secured. That helps secure the shaft should you break a U-Joint or something. you don't want the shaft to go over about a 30-degree angle.

 

[ptsg]

If you go that route, make sure your PTO shaft has a provision that lets it spin without coming off the splined shafts. That would turn into a real destructive mess with a shaft flailing around the output shaft of the tractor. There's been occurrences like this that took out the rear housing of the tractor--Very expensive repair.

Added: Another safety device is the PTO Shield. Make sure your shield chains are secured. That helps secure the shaft should you break a U-Joint or something. you don't want the shaft to go over about a 30-degree angle.

That's the great thing of that style of shear bolt yoke. The yoke has the standard 6 splines and push pin to lock on the shaft on the implement.

If the shear bolt breaks, one half of the yoke just spins on the other. To replace the shear bolt, takes less than 1 minute including getting the tools from the toolbox. Pull the broken halfs of the bolt out by hand, put new bolt and nut in and you're good to go.

Nothing like that mess that US implement manufacturers insist using on rotary cutters, where the broken shear bolt gets stuck on the input shaft of the cutter making a mess to pull out.