Thumb screw knob for M3 socket head cap screw - dome knob, 4 sizes 16/20/25/30 mm, no supports

A dome over a knurled band. The dome is deliberately flatter than a hemisphere: a true half-sphere would print at 65 degrees of overhang and need supports. Takes the head of an ISO 4762 (DIN 912) socket head cap screw M3 from the back. A hex boss in the pocket floor engages the screw's socket, so the knob turns the screw instead of slipping round it. The shank points out of the back, the front stays closed. M3 is the printer-bed levelling screw - the most common reason anyone prints a thumb scr…

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