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A source for shear bolts

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DRankin
Join Date: Jan 2000
Posts: 5116 Northern Nevada
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2002-02-03          35237

Does anyone know of an online or discount mail source for shear pins and shear bolts? I would like to get a dozen or so for my posthole digger before I really get to work with it.

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A source for shear bolts

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Bird Senter
Join Date: Jun 1999
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2002-02-03          35241

Mark, you can order shear bolts from the manufacturer of the implements (or at least I have for some in years past), but it really isn't necessary. Just take one of the shear bolts to a hardware store to match the size (unless you're already sure of the size, in which case you don't need to take one with you) and buy some bolts. I think most shear bolts are grade 2 and that's what you ask for (you might check your manual because there are some implements that recommend a grade 5 - personally I'd stay with the grade 2 to shear a little easier). ....

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Filip Vanzhov
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2002-02-03          35242

Hi Mark, The shear bolts that came with my posthole digger were just cheap bolts you can get anywhere. Definitely do not get the special hardened bolts that have special markings on the head. ....

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DRankin
Join Date: Jan 2000
Posts: 5116 Northern Nevada
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2002-02-03          35244

Thanks, I'll check my manual. Somewhere I got the notion that they were a special material..... maybe from the snow blower I used to have. I do know that it took specially weakened bolts. ....

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Bird Senter
Join Date: Jun 1999
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2002-02-03          35245

I'll bet those specially weakened bolts were simply grade 2 bolts. ....

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A source for shear bolts

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dsg
Join Date: Jun 1999
Posts: 528 Franklin, Maine
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2002-02-03          35249

Any shear bolt I've ever seen was just a grade 2 bolt. If something softer was need it would be a shear PIN which are made out of a variety of different materials, Brass, Aluminum, very mild steel and even plastic.

David ....

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A source for shear bolts

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DRankin
Join Date: Jan 2000
Posts: 5116 Northern Nevada
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2002-02-03          35250

Hmmmm.... The shear bolts for the snow blower had rings cut or cast into the shanks about where you might expect the shear forces the break it.... but then you are only dealing with an 8 or 10 horse gas engine and it might need more help than a 20 horse diesel with a vast (or at least a half vast) amount more torque. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2002-02-04          35275

Bolts are supposed to have markings on the head that identifies the grade. The marks are generally raised dashes that may be pointed toward the centre or I've also seen them lined up like hash marks. I think grade-2 bolts are unmarked. Dang, I used to know a web page that showed standard bolt marks.

It's good to know the marks. I broke a shear without having a replacement. I found the right sized bolt in a junk box and almost put in. Fortunately I saw the 3 marks that identifies grade-5 bolts. I also have bought grade-5 bolts in prepackaged sets from a box store that also sells auto parts, so I'd check the markings.

I'm guessing that a 100% proper shear bolt may be specialized to the extent that the shank goes all the way through the shaft, but I don't expect that a threaded portion in the shaft would make that much difference. However, any sloppiness or looseness in the nut will make the shear break easier. Sometimes you hear that the pin holes on old shafts that have broken many shears get 'egged' and then break the pins easier.

My 12" auger uses 5/16" grade-2. I checked with my dealer to verify the proper bolt grade, but I suspect that anything around that size that goes through the shaft on a 12" auger would be grade-2.

The pins on my snow blower are much smaller but they go through a collar rather then the shaft. I wouldn't want to guess the grade of these. A manufacturer may have used a smaller but harder bolts to gain more material on the collar around the pins. Still, at worst, a wrong grade-2 is just going to break when it shouldn't. Oh, it’s good to grease the pin shafts before installing. Real problem if they get seized in a shaft.
....

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David LaBrie
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2002-02-05          35318

Here is a link for Hex Head Bolt Markings.
David ....


Link:   Hex Head Bolt Markings

 
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Billy
Join Date: Oct 1999
Posts: 975 Southeast Oklahoma
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2003-02-15          49299

Hmmmmm...my tiller and rotary cutter both call for 8.8 grade shear bolts. When I cross reference metric to sae, the sae grade is 5. Most everyone says use grade 2 but 8.8 grade has a tensile strength of 120,000 psi and grade 2 is 74,000 psi.

Who is right here?

Billy ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-02-16          49331

I don't think it's all that uncommon for a manufacturer to use bolts harder than grade 2 for shear pins. Harder bolts are usually smaller in diameter for the same tensile strength so not as large of holes need to be drilled into shafts or flanges. I don't think a person usually can go wrong by sticking with a manufacturer's specs.

I think the 'always use grade-2 bolts' rule is simply because that's what's used a lot. If a person has any doubts about the grade to use then grade-2 should be the answer.

I'd probably stick with the metric ones unless I was in a bind, then I'd probably use a grade-2 SAE cross and see if I could get the work done before thinking about using a harder SAE bolt. For the metric ones, a tractor store may have a bin of them. If they don't most stores get regular calls from somebody called 'the bolt guy' Most stores likely would let a person leave a factory shear pin with them, get the bolt guy to identify it, and then order some in.
....

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