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Grade 8 bolts

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PAUL161

PAUL161

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I've always used grade 8 bolts on my equipment whenever possible, because of (shear) strength mostly. One of my tractors uses a through bolt on a PTO shaft that takes quite a bit of torque on the nut. I didn't have any grade 8 nuts left so I used a new grade 5, when torquing it up the nut stripped way before the proper torque setting and damaged the bolt threads. If using a grade 8 bolt, use a grade 8 nut! Just thought I'd put this out there for future reference. PJ
 
PAUL161 said:
I've always used grade 8 bolts on my equipment whenever possible, because of (shear) strength mostly. One of my tractors uses a through bolt on a PTO shaft that takes quite a bit of torque on the nut. I didn't have any grade 8 nuts left so I used a new grade 5, when torquing it up the nut stripped way before the proper torque setting and damaged the bolt threads. If using a grade 8 bolt, use a grade 8 nut! Just thought I'd put this out there for future reference. PJ
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Good advice - weakest link!
 
Another concern recently is where the fasteners are made. Shear and tensile testing may not be in the paradigm of some foreign manufacturers' processes. If that nut stripped and damaged the Grade-8 bolt before specified torque was reached, sounds like both are suspect.

Sometimes I wish I still had access to Charpy and tensile testing equipment.
 
Yeah I thought the same thing Doc, I try to get my bolts from Fastenel when ever possible, but their 20 miles away and if I need a bolt asap, I'll usually get one from our local hardware store that has the largest section of bolts in the area, but as you stated, where they get them is a question I don't know the answer to. Only bolts and screws I can't get around here is British sizes, they have to be ordered, usually from Brown & Gamons in the UK. They not only have the proper bolts but usually the proper thickness washers, most sell washers that are thinner than the originals and wrong diameter.
 
Paul
Good point on nuts bolts and many do not think about washers. I was in elevator construction for 40 years. Every thing was built on a factor of 10 By state and Fed. regs. Loads and shears related the
Earthquakes and general loading had to be at that factor of 10 ( as in 10 times ) The Nuts Bolts and Washers were all inspected and on Fed jobs even greater. Grade 8 was the normal on most all moving equipment
and cable supporting frames. The nut and washer work together and when you get into 1 2 or 3 inch bolts fit to bolt hole. I was also a Fed elevator inspector . Two cases I saw the review on that changed the trade for ever. Remember the MGM fire in Vegas. and the platform in ST Louis that fell with a 100 people on it That was support rods washers and oversize holes in beams that pulled through.
 
We used Wurth for most of our fasteners in the shop. The thinking was they had reputation to maintain. For applications on/in high stress environs where Grade-8 was spec'd, it was better to trust they were keeping standards than to assume any of the local suppliers were. And that trust in their materials was worth the added expense. Used Fastenal as well, same reasoning.
 
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