Jagwire POP End Cap for Compressionless Brake Housing Bottle of 10POP end caps are designed specifically for use with 5mm compressionless brake housing Not all frames or brake calipers are designed to accept a standardized end cap so the POP end cap acts as a reducerFeaturesReducer end fits brake calipers and frames that are not designed for normal end capsDurable alloy construction resists the increased stresses of compressionless brake housing