Sold individually, this thumbscrew only fits the 5514 Kahler Deluxe String Lock and is only available in black.
Lightly tighten this thumbscrew just before you flip the levers over the detent and snap into place, locking the string pair. It passes through a 9426 washer, a 9424 wedge, the base and finally into a 9535 clamp plate which gets pulled up to clamp the strings.