"These are special cord locks with the whole part acting like a spring. The C squeezes together and the cord is inserted into the hole. Fits up to 1/8-inch shock cord or 2 1.75 mm cord. I am calling them Darth Vader and 3CPO after the characters they look like."
 
The above-quoted wording is straight from Dutchware's team.
 
This is the smaller Springless Cordlock,  3CPO. We sell these in sixes.