Referencing photo 3, the small knob projection at nine o'clock position that is the hinge of a machinist's compass scribe. The arm with the knob had a pointed arm attached to it. That was the center arm and was held against the central point of the drawing/model by the knob. The other side had an arm with a hardened point on it and was used to scribe the measurement or arc. Great for bisecting circles or measuring off segments of a line. I guess it might have been used to calculate artillery elevation?
The other item does look like some kind of a tongue and wreath design but perhaps a ladies garter clasp?