Upgrade your drill top table !!! Quick Release System Top Table with Extension

[Frank S]

Those appear commercially made clamping straps. Not one of the woodworking variety slot them a reasonable distance to gain clamping leverage; if anything the opposite of 'gain'. The lack of spherical segments under fastener to create flat plane is another shortcoming.

A perfect application to use some spherical rocker are spacers from the valve train of GM engines

[Toolmaker51]

Those [GM rocker balls] would work well. They're probably 10mm now, older were 3/8". In a pinch we drill centered through short piece of round stock, top milled flat.