Sometimes you want to put a ball winder on an edge of a table that's not perfectly square. Maybe it's bull-nosed or has a weird lip on it. Despair not! A cheapo jar opener can help keep the clamp from slipping off and sending your poor winder flying. (If you care a lot about the surface, be sure to check to make sure said jar opener isn't degrading and melting itself onto your table/bar/whatever every couple of weeks.)
P.S. - Are you coming to Yarnover? Come see me! I'll be at Saga Hill Designs.