i have been given some wheels, but my standard wheel nuts are too big, i need some small 20mm or less to go in the holes.

can anyone help me out

If they are aftermarket wheels it is not uncommon to have to fit smaller wheel nuts (acorn nuts iirc) to clear the nut recesses. Your nearest wheel supplier will have stocks so its best to give them a call.

Or try Scarborough Racing Developments

or try scrappy