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Substitute Grade 8 for 2H nut and bolt

Substitute Grade 8 for 2H nut and bolt

(OP)
Should be a simple question but I wanted to check with someone with more knowledge of fastener strength than myself.

I took off a trailer hitch (on a 17 year old) motor home and am now re-installing it.

To my surprise, there was three types of hardware used ... all 1/2" fasteners.

1) two grade 8 bolts (one on each side) holding the bracket to the frame

2) two ???? grade carriage bolts (with 1" x 1" custom washers ... square hole) with 2H nuts hold on the other end of the bracket (the back end that takes most of the load).

3) four grade 5 fine threaded bolts with flange nuts holding the bracket to the receiver cross member.

I was about to replace all the hardware with standard grade 8 hardware. Obviously this is no problem with the ones that were originally that. It won't be any problem with the four that are fine thread (these actually just lock the tube with to the bracket and need minimal strength. I am thinking the fine threads and flange nuts were just used for convenience since the flange nuts are inside the cross member tube and it would be hard to impossible to side a washer, lock nut and nut 6" down inside the tube.

My worry is with the two carriage bolts. Is there any reason that the two carriage bolts ( I can't tell their grade ... 17 years of salt and rust have taken it's toll) with the 2H nuts can not be replaced with grade 8 hardware (bolt with washer on one side and washer, lock and nut on the other)? My "guess" is that this will be OK since a 2H nut has the strength of about grade 5. My best "guess" is that they used a carriage bolt just because it was easy to install. The square washer bottoms against the frame and a wrench is not needed. This is not a problem on my motor home since I have lots of room to get a wrench on top and bottom of the bolts.

Thanks ..... Mike


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