Kcnc replacement crank bolt end caps - also available in anodised Silver, Red and Black.
These are the gold version of end caps that come in black as standard on Kcnc XC-1 ISIS and K-type cranksets - they just look nice!
They fit into the cranks after the crank bolts have been torqued up to prevent the ingress of dirt, and also to act as self-extracting caps when the arms have to be removed. >