Which SAE Grade Hex Bolt Do I Use?

rancar · Mar 6, 2003

OK....here's a question for you machinists and hardware techies .....

I'm rehabbing an old carryall for my JD4710 tractor. I recently had to have new lower lift pins custom made due to the old pin's incompatibility with the ball and socket ends on the lower draft links. The lower lift pins are housed in a bracket assembly that is bolted onto the carryall's frame. Two bolts fasten each bracket assembly to the frame's sides...four bolts total.

The old Hex bolts were 1/2" by 3 1/2". I intend to retain the 1/2" diameter since I don't have the tools to re-drill larger holes in the carryall's frame. The lift capacity on a JD 4710 3PH is 2,500lbs but I don't anticipate carrying anything greater than about 1,500 lbs (new custom made pins were threaded for this load capacity). I'll be using the carryall primarily to haul logs out of the woods and fieldstone out of the hedgerows.

Now, the question:

What Hex bolt SAE grade is recommended for this kind of assembly? I can't bring myself to use the fragile SAE 1 grade products I see in Home Depot due to safety concerns. I don't want to see these bolts snapping off under heavy loads. I've thought SAE 5 grade would be sufficient. SAE 8 grade sounds like overkill and are quite expensive possibly requiring me to buy a whole box of these which I don't need.

Anyone have any thoughts on this issue? Thanks for any input.

....Bob

Hoeman00 · Mar 6, 2003

I'd go w/ the best available, at least gade 8, u aren't looking at the shock load that these could be subject too.
U don't have any one local like a bolt house or ? that sells in less than box lots?

Anonymous Poster · Mar 6, 2003

Bob,
Tractor Supply Company (TSC) sells Grade 8's individually (by weight.) Might give you the strongest bolt with the least cost.

cowboydoc · Mar 6, 2003

I just bought some grade 8's, metric 14x1.5 and they were $1.20 per bolt.

herbenus · Mar 6, 2003

I'd only go grade 8. I wouldn't buy bolts for this from home depot. You should be able to find a place that sells a few. I didn't know about Tractor Supply. I'll keep that in mind for future projects.

rancar · Mar 6, 2003

<font color="blue">"...U don't have any one local like a bolt house or ? that sells in less than box lots?...</font>

I'm finding it difficult to find Grade 8 at local hardware stores around me. They go to grade 5. I can get Grade 8 online but they sell them in boxes of 3-4 dozen or thereabouts. I can likely get what I'm looking for in local machine shops but these guys don't sell retail. I'll check out TSC though. Thanks for the tips gentlemen.

....Bob

hazmat · Mar 6, 2003

Bob,

When designing/building in small quatities (eg 1) you waste more "money" thinking about it than just buying the better bolt.

McMaster Carr has Grade 8 1/2-13 X 3.5" for $7.95 /box of 10 (plus shipping). You could probably get them at a local hardware store or look under "industrial supply" in the yellow pages. Like the commercial used to say, call ahead.

For fun here are the calcs you would do.

Grade 8 has a min tensile (pull) strength of 150,000 psi, grade 5 is 120,000 psi.

Sounds like you are loading them in shear (bolts are weaker in shear than tension).

Assume that bolts are directly in line with lift pins, if they are offset, then we need to do some moment (torque) calcs.

2,500#/4 bolts / .196in^2 (xsection area) = 3,000 psi shear stress. Grade 5 or 8 will do nicely.

hazmat · Mar 6, 2003

Forgot the "cost" calc.

10 minutes for me to write the previous post. They bill me out at $105 / hour = $17.50 = more than the bolts cost.

PS the p/n of the bolt at Mcmaster is 91286A339

hazmat · Mar 6, 2003

<font color="blue"> I'm finding it difficult to find Grade 8 at local hardware stores around me.</font>

try the aforementioned "industrial supply" or NAPA.