Severne Windsurfing Boom Wave Cup
Severne Enigma carbon booms and the Metal aluminum booms come with a front end that is dedicated to either a standard diameter or reduced diameter mast. If you have a larger size boom (160cm or bigger) and want to make it dedicated to a reduced diameter mast, this is the part you need. You replace the slalom cup (just the part that fits around the mast on the boom front end) with this RDM cup and you are ready to go.
This switch requires unscrewing the front end from your boom, it is not an easy-on/easy-off shim.