Stayput Toggle Tarp Fastener - For 3/8 inch Grommet Hole Size - 10-Pack

Works great 1/2 in grommet so I had to add washer would be great if you could have one manufactured that would work with a1/2 in grommet without having to add flat washer

This little tarp fasteners are great. They are a little expensive but worth it. We ordered clear tarps for a patio and used them for this.

Works great easy to use easy to install