https://www.sonos.com/en-us/shop/beam.html
Threaded mount
1/2 in. (12.7 mm) / 10-32 threaded mounting socket.
Thanks for the feedback. I also spoke with a Sonos Sales Rep. He stated that the Beam has standard M5 threads for the bolt holes measuring 3.9 mm deep. Since I could not find the exact match, I purchased several from Home Depot. The one that fits perfectly is Everbilt Machine Screw M5-0.8 x 12 mm. The Beam is now secure to the mount.