TARP SPOOL C HOOK

Tarp Spool Hook: Tarp spool hooks are bolted onto the front and rear of the trailer on the driver side a roll stop for the tarp roll tube.
Secures the roll tube in the closed position as the roll tube rolls into the cradles at the opposite end of the trailer
Supports the roll tube during transit down the road in the tarp closed position

Tarp hook does come with the bolts to mount it on the tub. 

Hooks are sold individually; you'll need 2 per trailer.
Cradles both ends of the roll tube to keep wind from trying to pick the system up; or move the system around; holds it firm in place