i bought my rc12 used and it didnt come with the thick washers. i bought a bag of radio shack washers and im using the biggest size. i really havent measured the thickness yet but theyre a bit thinner than the stock rc12 washers. im not sure about the quality of the radio shack washers (some may be a bit thicker than the others because of the chrome plating) so you may want to choose 4 of the same size and sand them down so all 4 will be uniform in thickness.