Hi there,
For the wireless rear speakers on the HW-Q930B Soundbar the surround speaker wall mounts must be able to support more than 17.6lbs.
Hole size on the back of each speaker: 1/4 - 20 UNC threaded insert
You'll use a standard screw: 6.35 mm (0.25 Inch) with a 1.27mm (0.05 inch) pitch, and a length of 18mm (0.70 inch) long.
~Samsung Solutions