Bush hog SQ60 - what shear bolt?

[timsch]

I need to order some shear bolts for my Bush Hog SQ60. I can't find the specs for this online. A general search finds most recommendations for shear bolts for shredders are grade 2.

Looking specifically for my model, I get hits for the Bush Hog SQ160, which looks pretty comparably to mine, which shows Grade 8.8. Holy smoke, that's a difference. So... I figured I ought to ask y'all before ordering something and getting it wrong. The thru-hole is 7/16" diameter.

I'm pulling it with my Kubota L275DT and am mainly shredding pastures, FWIW.

 

[timsch]

Just doing what I should have done last night rather than posting, was to calculate the shear strength of a grade 2 bolt and match it with that of the gr. 8.8 bolt using the formula: shear strength =0.6*min_tensile_strength*bolt_area

An 8mm Gr. 8.8 bolt has roughly the same shear strength as a 3/8 grade 2 bolt, so that's what I'll go with.

 

[Texasmark]

I like to use Grade 2 bolts sized to fit the hole on my shredder mowers. I liked them because they smear as they break which is easy to find on the shaft. The other thing is that I don't run the nut down tight as using a lock nut and leaving some slack seems to allow for some wear between the drive and driven parts of the joint and has resulted in fewer breaks.

My JD 375 round baler specifies a 1/4" Grade 8 which I have broken a few times and it "snaps" when it breaks leaving no smear to try to find.....but for some reason it is easy to spot on the baler input shaft.

 

[Ray,IN]

I like to use Grade 2 bolts sized to fit the hole on my shredder mowers. I liked them because they smear as they break which is easy to find on the shaft. The other thing is that I don't run the nut down tight as using a lock nut and leaving some slack seems to allow for some wear between the drive and driven parts of the joint and has resulted in fewer breaks.

My JD 375 round baler specifies a 1/4" Grade 8 which I have broken a few times and it "snaps" when it breaks leaving no smear to try to find.....but for some reason it is easy to spot on the baler input shaft.

I totally agree; I want the cheapest, easiest thing to replace, to break first. I carry spare gr 1 bolts in my toolbox for when using a brush hog, baler, etc.
Bolt strength by grade:

 

[BarnyardEngineering]

Just doing what I should have done last night rather than posting, was to calculate the shear strength of a grade 2 bolt and match it with that of the gr. 8.8 bolt using the formula: shear strength =0.6*min_tensile_strength*bolt_area

An 8mm Gr. 8.8 bolt has roughly the same shear strength as a 3/8 grade 2 bolt, so that's what I'll go with.

8.8 is the metric "equivalent" of SAE grade 2, so yeah, that checks out.