The top mount allows musicians to bend the pitch of notes or entire chords with their pick hand for various effects. The Bigsby Vibrato was the first successful design of what is now called a whammy bar or tremolo arm, although vibrato is technically the correct term for the musical effect it produces.
We have a number of these Gold B-50 Bigsby units available for sale. These were manufactured a few years back, but have been sitting packaged away in our warehouse and have never been used.
*Designed for use on flat-top electric guitars.