The end cap is designed to be glued or epoxied into the hole at the end of a handle. A hole is provided to allow the use of a lanyard made of cord or strip of leather. The end cap has been designed to fit into 5/16 inch diameter holes although depending on processing it might fit into smaller 1/4 inch diameter holes. Always measure your parts before drilling.
A smoother version of this design is available and may be found
here:
https://www.shapeways.com/product/C9SQPG68N?key=5cc0f39807658d232b6ad340d507a54c