(Note: Measurements are outside max. dimensions unless stated otherwise).19th Century : Decorative knob with geometric spirograph decoration around central raised dome.Top diam. 25mm. (1")Height 21mm. (13/16"). + screw shaft 13mm. (1/2")Collar diam. 12mm. (7/16")Tapering top side walls.Note: made in 2 parts and soldered at top of rim. Thin joint line may be apparent.For suitable backplate if required, see "Backplates" section.It is recommended that if selecting screw thread option, a pilot hole is drilled and pre-cut with a steel screw of slightly smaller size before screwing in the casting to avoid shearing.