Originally Posted by
WickedThump
The way this one is designed varies from the angled plug I see on quill stems. On this one, the plug is a round taper and expands a split sleeve against the tapered end of the post such that the sleeve expands evenly. It came out dry, so I need to grease it up and put it back.
There are several quill stems that are designed with expander plugs like the one on your seatpost so it isn't a unique item. The angle adjustment saddle clamp is also a common type found on lower-line and some mid-line seatposts and usually referred to as a Laprade type.