It's the only game in town if you own an older SID fork. I have 2 of them and love the forks but they do need this special adapter for air / - adjustments. It is a nicely made unit but should have been made of brass. The alum threads keep me from messing up the tiny threads on the fork itself but are prone to stripping. I bought two of these adapters in case I did strip it. So far, so good.
A word about Treefort: They shipped very quickly and packed the items extremely well. They made a special effort to accommodate my unusual shipping address. Nice folks and they deserve a 10 for customer service.