This is the 'gland nut' that you are talking about....tighten it down with a spanner and the leak should cease. If it doesn't, undo the nut and wrap PTFE tape around the tap shaft, and press it in by screwing the nut back in. In no circumstances undo the large hexagon that holds the tap into the body though, or you'll be swimming for it! If you do the gland nut up too tight, the tap will be difficult to turn on and off. Hope this helps!
John
March 2009
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