unifiber hd aluminium sdm extension 1Introducing the Unifiber HD Aluminum SDM Extension. If your sail requires high downhaul tension, the HD SDM Extension is the right tool for the job. The base itself is made of high quality polyamide to withstand the high tension of the downhaul. With a 3 roller pulley, the Extension reduces the effort you need to trim even a slalom sail. The functional length can be adjusted with one hand using the collar.