Argh! Core support bolt square washers are turning.

[In The Ten Ring]

I was afraid this would happen. I have the body mount hardware kit from Classic Industries and I thought the core support square washer was a bit small. Mine are turning instead of locking up against the side of their core support recess. Anyone else experience this?

I am going to go out here in a bit and see if Tractor Supply has a grade 5 standard bolt I can substitute.

*3 tick marks on a bolt head is "grade 5" correct?*