I am not sure what it is but I don't think that it is a rivet bolster. With the shape being what it is, it looks like it would really ding up whatever your tyring to rivet together.........ken
This rose, the leaves and the stems are all made out of the triple roller chain that the rose is framed with. Forge welded into a billet and forged down to 16 gauge sheet and 5/16 round.