This is the selector knob for the Quad AM3 tuner. Each tuner has two: one for the waveband, and one for the filter.
This product is best ordered in pairs, so both knobs match cosmetically.
6mm M3 grubscrew required, aligned with the top flat on the shaft, and tightened with a 1.5mm Allen key. Some trimming may be required. Holes may be slightly undersized for production reasons: shaft hole is 1/4", grubscrew hole is 3mm.
Reassembly is a bit tricky. First fit the selector knobs into the front panel from the back and top, laying them slightly sideways to fit. Then straighten them and offer the front panel up to the tuning knob. It may be possible to introduce a couple of the four 4BA panel screws at this stage if they are long enough, threading them just far enough in to locate the panel. Now, by wiggling its outside end, introduce the lefthand selector knob over its shaft, then the righthand one. Lighty tighten the grubscrews from the top. Now introduce all four panel screws from the rear. Do not tighten any of them yet. Now check that the bezel has engaged fully with the slot in the front panel. A light tap in the required direction(s) will locate it properly along all four sides. Now tighen the selector knob grubscrews and then the four panel retaining screws.
For strength reasons the product is only offered in aluminium, which also provides a reasonable colour match.
Note that the selector knob for the Quad AM2 and 'half-moon' tuners are different.