Here's the classic fluted Boss knob. It's got a metal top with a circular ring pattern. It's got a brass insert and a set screw.
Measures 33mm x 16mm
Shaft opening 6.3mm
Note:
I've got 5 different sizes of classic fluted Boss-style knobs, from extra-small (20mm) to extra-large (44mm). Check out the measurements below for a size comparison.
Extra-small: 20mm x 11mm
Small: 23mm x 12mm
Medium: 27mm x 15mm
Large: 33mm x 16mm
Extra-large: 44mm x 19.5mm
All shaft openings are 6.3mm.