Some 1/8 thick washers and believe it or not ,you can use a hack saw ,sawzall etc... to cut the rubber thinner. I cut the standard mount down to a little under 1/2 .I only got 3/4 of a inch or so drop,but it cost nothing extra.The main thing is some sort of soft pliable long lasting material to keep the squeeking down and provide body to frame clearance so no contact is made when a uneven surface is driven on. good luck