On Saturday, June 20, 2020 at 4:59:06 AM UTC-7, David Cleveland wrote:
Referencing Chips comment about using harder bots. He is absolutely correct. Many trailers I've seen, mine included, have multiple washers at the mounting point to move the strut and spring arms out away from the trailer. Use caution.

Metric bolts have a different hardness grading system. A metric bolt marked 8.8 is the same hardness as an SAE grade 5. If you want to upgrade the hardness of a metric bolt, use a 10.9 or even 12.9. Frank's comment about using a large diameter bolt would be a good idea as well.

If you can't find metric you could use 5/16" grade 8 bolts these are only .0015" smaller than an 8mm basically the same.
McMaster Carr has a selection of grade 8 both the carriage bolt that is used on the bottom end and the hex head used on the upper. Also use the nyloc nuts. Highest grade they offer on the carriage is 8, 10 offered for the upper bolts.

They have the both metric bolts in the 8.8 or Grade 5.

Richard
www.craggyaero.com