ccmarco
i had the same prob as you , i had a 12mm diameter trapezioid screw , so i turned the screw down to 8mm using a grinder and a drill as a lathe , threaded the end for a locknut , used a 100mm x 100mm x 10mm plastic shim with a 22mm hole drilled in it( to take a skate bearing) as a bearing block. so it went , thrust washer - bearing block (with skate bearing ) - thrust washer - locknut , tighten locknut to preload assembly , solid and cheap i have no lateral movement in screw ..... phew!!! maybe a pic would have been better