that's a beautiful 28. It looks to be in great shape. That extra bob at the bottom was something that was done on machines up until about 1910 on 20 somewhere in that range depending on the company. they were trying to show that sewing machines made stitches as good as a hand stitch. A seamstress when making a stitch would give a little tug to make the stitch tight. That's what that bob is doing, it is helping just snug the stitch. This is one of the reasons that early machines actually sew better than modern machines.