Some of the Harken Winches have screw on tops. The problem with this design is that it is hard to tighten them and over time when ever anyone puts their hand on the top of the winch to steady themselves they invaribly end up loosening the top. At the most in opportune time the screw top flies off and you are in the middle of a race without a winch. Bad….. What I learnt is to use an awl to punch a little hole in the top of the screw on top. When you finish servicing the winch just give it the extra tap with an awl and hammer and it is less likely to undo.