You want to be able to hold delicate or crushable parts in your vise, but those hard steel jaws don’t scream “delicate.” You could wrap the parts in a rag or use some other awkward method of cushioning them — or you could slap on a set of Soff Jaws.
Zona Tools designed their Soff Jaws to attach magnetically to any 3″ or 4″ ferrous-jawed vise. The cushioned jaws grip odd shapes, prevent marring, and stop the jaws from crushing softer or delicate parts.
You can get Soff Jaws with either leather or vinyl acetate jaws. Both versions retail for $8.