1/4" stainless carriage bolts, 304 passivated stainless, minimum yield strength of 45,000 PSI.
Each bolt has a minimum yield strength of 2,209 pounds. Even at a fraction of that strength, I've got six bolts holding down my load (three hold downs per machine, two bolts per hold down)... I think I'll be fine.
I'll use either a pair of large washers (fender washers) or a square metal plate on the bottom side to spread the load out across the plywood floor, which I suspect will be the limiting factor in the amount of load each hold down will support.
- Frank
1984 200ES Big Red
1985 350X (x2)
1986 350X
1986 250SX
1984 Auto-X
1984 ATC70
1985 ATC70