Brass piston works at the base of the RX-20 in conjunction with the handle lock assembly. This is a newer style that measures a little shorter than it's older counterpart. This piston has no collar.
This piston when engaged by the locking clamp applies steady pressure to the handle arcs and this is how the handle assembly locks in place.
This is an updated style plunger, which measures 1.535" as opposed to the older style that measures 1.568". The two can be differentiated by the lack of collar at the top of the updated plunger. These are not interchangeable parts. If employing the longer plunger with collar (HM-107101-EA) where a shorter one is required the clamp won't be able to clamp into place it'll hang up.