The new TOWNER Down Tension Bar II provides the necessary tension to keep your strings in place. The reason for the 2 thumbwheels is to have one pair hold the DTB ii in place and the other two to manage the height of the bridge.
Towner String Tension Bar II Steel
Bigsby B3 Silver Tremolo Vibrato With Towner Tension Tension Bar & Fittings
Towner Gold Plated Aluminium Down Tension Bar & Hinge-Plate Adapter
Gold Down Tension Bar + Hinge Plate, TOWNER no drill adapter for BIGSBY
TOWNER No drill Gold Down Tension Bar adapter for BIGSBY
TOWNER Adapter for BIGSBY - Down Tension Bar No Drilling!