Skirted Tuning knob
Fit controls with 6.35mm (¼in.) shafts with D Flat
Colour Silver rim 
Material: phenolic plastic
Push fit
Large diameter 3" (75mm)
Mirror center diameter 38mm
Bush diameter 9.5mm
Bush length 15mm
Side lip depth 7.5mm
Panel hole required 10mm for knob bush to pass through panel 
An unusual type of knob for this day and age. Limited to available stock.
The outer part of the knob is in the same mirror finish (chromed) and the outer co-axial ring is a window, useful for protecting panel legend while viewing through the knob window. A line can be scribed on the underside of the window part to give a pointer reference.