This is a bushing (bearing)


it slides into the end of the stuffing tube, the collar stops it from going to far into the tube, if you look at the end of your strut the brass part you see in the end of it is the collar of the bushing, IF you didnt have a bushing in the strut you would know it as there would be a lot of play. Hope that helps a little

Might add, the collar of the bushing is approximately the same size as the stuffing tube itself.