Strange Musicman bridge..

I just bought a used 1994 Stingray.
The bridge is weird, never seen such a bridge on a Musicman.
It is a true Musicman part because it's engrave 'musicman' on it exactly the same way as normal bridges..
The bridge has 4 plots to set the high of 4 felt squares, to stiffle the sound..
Has anyone tried this ??
Is it a rare piece ?
I'll send pics as soon as possible.