Improved Spool Retaining Nut for robkar's PSMSHWSPBB&TL

Neither of the 2 original nut designs for robkar's spool holder would work with the very reasonably-priced Hatchbox 1kg filament spools or 0.5kg 3D Solutech spools due to their small spool hole size. In fact, the smallest size supported by the "small" nut design by rokbar is identical to that of the larger default nut.

This improved spool retaining nut design will work with any size spool center that will fit on the holder (approx. 25mm - 68mm). Multiple retaining nuts are not required. Th