After years of problems with commercial cord locks & much trial & error, the lion kingdom finally arrived at a promising design for custom ones.

The mane problems with commercial cord locks were lack of grip on new string, difficulty installing the string, limits on the size of the string.  The trick with the custom ones is they're sized for exactly 1 string diameter, through painstaking trial & error.  Experience with cord locks showed they could provide just enough grip to be useful while still allowing field adjustment.

Currently, they're sized for 10 passes of #18 mason line.  

The big unknown is how they'll behave when the string ages & expands.  Will the string still be adjustable.  They could be made of TPU to emulate the compliance of a spring.  They're removable after assembly & are pressed together by the same friction that grips the string.  They've proven less prone to causing chafing, despite the sharp edges.  There's finally the possibility of reusing string.