Davetnova was right about the Aspri; I have had one for years and it is a hoot to use. It is essentially a black plastic box that contains a metal bridge affair that slips under the guitar's strings just prior to the bridge, and is pulled back to the butt end of the guitar to tension the three springs inside the box. The metal bridge has to be bent some to exactly match a compensated bridge, but once adjusted, it slips on and off with ease.

The sound is like an old Stratocaster playing "Wipeout". When I put it on my 12-string it sounds like a bouzouki on steroids. They stopped making it in the 80's, but if you see one in a pawn shop, pick it up; you can use it on slip jigs like the "Butterfly" and have a ball with the Hammered Dulcimers.