Trailer coupler bolts
 

Just installed eoh kit on my trailer. In doing so, I put a new coupler on. The surge coupler used 5/8 bolts, the new coupler has 1/2 inch holes. I got grade 5 hardware for it. Will these suffice or would grade 8 be better? Store only had grade 5.
Trailer in question is a triple axel under a formula 353.

I would for sure use Grade 8 bolts.

Absolutely get Grade 8 bolts.

Grade 8 and the larger size.

Thanks all. Ordered the grade 8 and I'm gonna exchange the buyers coupler for a demco.

Call the coupler mfg and ask them about drilling out the 1/2' holes to 5/8...your better off with larger hardware if possible...
As for grade 5 or 8....i think there can be a good discussion about this from both sides.....keep in mind that tensile strength is the pulling/pushing force on the bolts threaded axis. These are not trying to keep cyl heads on the block from coming off. On a trailer application you are talking about shear from the sideways load on the bolt. A grade 8 bolt is stronger but at the same time its harder and more "notch sensitive" meaning its more prone to stress buildup in areas that are nicked or notched and will lead to failure...like in the case if you used a 1/2" bolt in a 5/8" hole and the coupler was moving back and forth hitting the bolt and nicking it. A grade 8 bolt will always win in the strength dept...but ive seen some weird things in our machine shop where grade 8 bolts kept snapping from shear where as a grade 5 would bend and deform and still keep it held together....

I've been reading similar things on the interweb. The Demco coupler has 5/8 holes where as the Buyers has 1/2, which I overlooked when ordering.
Maybe I'll put one grade 5 and one grade 8 when I install it. 😄

If I understand the situation correctly, the holes in the coupler are 1/2" dia and the holes in the trailer tongue are 5/8" dia. If thats the case, I'd find another coupler that uses 5/8" bolts. I seriously doubt the coupler manuf will approve drilling out the holes. Why would they? Their risk/reward ratio would be completely out of balance. If they did approve it, I'd want it in writing for sure, but even then, they could day you didn't drill it correctly.

Is regards to grade-5 vs grade-8, there's a lot more to it than which is stronger. Corrosion resistance being one example, ability to bend vs break is another good point made prev.

Obviously the application factors in a lot but I personally like Grade 5 hardware...for many of the reasons listed above. As far as the coupler is concerned, I would go with 5/8" Grade 5 and sleep/tow very happily.