AM19-2US provide exact same geometry as AM19-2.
This new part is made from 3mm thick 7075 T6 high grade alloy, which mean it's 0,5mm thicker than AM19-2.
To keep same rollcenters on toplinks like with AM19-2 its needed to run 0,5mm 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.