Terry brought next idea :
replying to Harry Bloomfield, Terry wrote:
y thought is to use old bike tyres with thick tread cut sized pieces from it
and glue and screw to bottom **

I usually avoid responding to HOH posts, but six years on - my bench
legs are absolutely fine with the bolt heads keeping them clear of the
concrete slabs it sits upon. It doesn't need any adjustment, because
its own weight forces it to give enough to sit with all four legs down.