This is a replacement HeatBreak for E3D-v6 1.75mm Universal HotEnds.
Since v5, the manufacturing processes for all our HeatBreaks has been overhauled to achieve a better internal surface finish than ever before. The improved internal surface finish will help to reduce extrusion force and improve relliability on retractions.
This v6 HeatBreak is not compatible with it's v5 predecessor on the cold side (i.e. the heatsink).