Shear bolt size

[foggy1111]

I just picked up a new Woods Stump Grinder on Saturday from a dealer about 20 miles away. I am busy hooking it all up....BUT they did not include a bolt to hold the PTO shaft onto the gearbox (the slip-clutch hub to the splined gear box input shaft).

The parts manual shows this size data for the bolt: M12 x 1.26P x 60 mm HHCS & nut.

I'm not certain if the above description tells me a bolt strength (HHCS ?) and I'd like to spec the right bolt so I don't bugger things up. (I'd go back to the dealer...but I don't want to drive 40 miles over a bolt.)

Enlighten me please?

I wrote "shear bolt" for the title....but it is NOT a shear bolt. I cannot undo the title. Sorry.

 

[nickel plate]

Hex Head Cap Screw.

 

[kebo]

If properly adjusted the slip clutch should take care of any rotational overstresses on the PTO shaft, but I'm sure you know that. Unless you think it really needs to be a high strength bolt for this use, I would slam a metric grade 8.8 bolt in there and go with it.

 

[foggy1111]

Thanks.....and here I thought that there was some secret to HHCS. :laughing:

I will pick out the equivalent of a grade 5 bolt. crank on it....and let it rip.......errrrrrr grind.

 

[greg_g]

If the slip clutch is splined to the implement transmission input shaft as you describe, the bolt hardness really doesn't matter. There is no rotational torque on the bolt in question. In this application, that bolt is merely a fastener; its only job is to keep the clutch from pulling away from the transmission input shaft. But the bolt diameter is important. Make sure it's a tight fit through all four bolt holes. Otherwise the shock load can bend it. When that happens, the bolt holes start elongating (egging out). Also shop until you find a smooth bolt that's only threaded on the portion that extends beyond the outside hole. Don't use a lock washer, snug up self-locking (NyLoc) nut instead.

//greg//

 

[johnrex62]

Grade 5? I have been told that without a grade specification a grade 2 is implied.

 

[RoyJackson]

The parts manual shows this size data for the bolt: M12 x 1.26P x 60 mm HHCS & nut.

M12 is a 12mm thread (12mm diameter).

1.26P is the thread pitch (BTW, this is probably 1.25...that's a fine thread and to the best of my knowledge, there is no 1.26 pitch).

HHCS is Hex Head Cap Screw.

And, no, it doesn't specify the grade of bolt. That means it's a standard grade (Europeans don't specify grades unless it's something special.

 

[kebo]

Grade 5? I have been told that without a grade specification a grade 2 is implied.

You're thinking shear bolt! This is not a shear bolt, the title of the post is misleading! Metric bolts are graded differently on hardness.

 

[foggy1111]

M12 is a 12mm thread (12mm diameter).

1.26P is the thread pitch (BTW, this is probably 1.25...that's a fine thread and to the best of my knowledge, there is no 1.26 pitch).

HHCS is Hex Head Cap Screw.

And, no, it doesn't specify the grade of bolt. That means it's a standard grade (Europeans don't specify grades unless it's something special.

My bad. One misleading (shear bolt) and one thread pitch (1.26) in the same post. I'll do better next time.

 

[leonz]

Use a metric Nylon nut or Blue Loctite only.