Dave, I would suggest you put a regular washer, then a lock washer on the screw attaching the QS8s, for safety. Don't want to switch on the Eleven O'clock news....Man killed by falling quadpolar speaker, it is believed while listening to "Master and Commander" at 105db, a screw came lose on the bracket, causing the speaker to fall and beaned the unsuspecting victim on the head.

Half of communication is listening. You can't listen with your mouth.