AM19-FX-US Upper Arm Holder for A800FX FWD and A800MMX car.contains 2pcs A800FX-AM19-FX-USAM19-FX-US provide exact same geometry as AM19-FX. This new part is made from 3mm thick 7075 T6 high grade alloy, which mean it's 0,25mm thicker than AM19-FX. To keep same rollcenters on toplinks like with AM19-FX its needed to run 0,25mm less shims under ST24 Ball Studs.Info: Parts with "US" designation are especially designed for the use at tracks with hard boards/barriers. During the different design compared to the standard parts, the "US" parts are more reliable at impacts. Basically this optional parts are a bit more heavy than standard parts.