Curious bolt in a Fillmore 25

[Peteoh]

So just received a used Fillmore 25 and noticed this Phillips head bolt hanging there. It doesn’t want to thread in or out but is loose to rattle around in the chassis hole ??
I can fit a grommet to it to silence it, but what is it for ?

 

[woodbutcher65]

Chassis tensioner bolt. It presses against the cabinet and helps damp out chassis vibrations which can be a problem at high volume.

A fair number of amps use that idea.

Loosen it when removing the chassis from the cabinet. After reinstalling the chassis, snug that screw up firmly.