For those of you who aren't in the know, here is a good tip from a long time Turner Summer Ski owner.
Use Stainless Steel Hex Head bolts with a "Sealing Washer" under the Hex Head (rubber side toward the board) and then a Stainless Steel Washer on top of the baseplate and a Nylock Nut over that.
The "Sealing Washer" is a slightly conical washer with a thin layer of rubber bonded to one side of the washer. This rubber layer will help isolate vibration (in theory) preventing the hardware from maring your gel coat finish and the conical shape will "flatten" and spread the tightening load to the top layer of your foam fiberglass construction slalom board.
Tighten the hardware until the washer just goes flat or until you see the top layer of the board just starting to depress, then back off slightly.
This is the culmination of years of searching many hardware stores and many conversations with other foam fiberglass construction board owners.
Now you know...
Foam Fibreglass Construction Slalom Board Mounting Hardware
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