not an expert on trigger guards, but in the middle right hand picture, the half circle hole on the right end of the piece looks like it should go over a pin. likewise the area just behind the 'trigger' shaped object on the left of the picture in the top left and bottom left pictures, looks like it too should go over a pin, and they are in the same plane. Just to throw in for a different guess, it looks to me similar to the latching mechanism for the fore stock on a single or double barrel shotgun??