The early Alpha Antennas magloop (the aluminum segmented ones, not the coax loops) uses a rather abysmal knob to tune the resonance capacitor.  This is a quick and dirty print to slip over the knob itself, to save your wrists and make tuning easier.

Given the, uh, “bespoke” quality of my copy of the antenna, I'm not sure whether or not these knobs were used universally.  It's a 7-sided knob, just over an inch in diameter (27mm or 1.0625" or some other weird number, to match the weird seven-sided-ness.)

The model should be pretty easy to tweak in FreeCAD if you need to, or as easy as anything is to tweak in 3d modeling softwares.  It's not a huge difficult to re-do the model if you need to for your antenna.  If you make one, let me know and I'll happily link to it from here, so people can find the appropriate files for their antennas.