Electro-Voice Rough-In Mounting Plate - For C8.2 & C8.2LP Speakers - Pack of 4
Details
RR series plates are made of flat sheet metal with holes to attach to the joists or trusses of a building structure. The holes are drilled for nails or screws at 16 inches (406mm) 20 inches (508mm) and 24 inches (610mm) on-center. The installer can drill other holes as needed up to a maximum of 24 3/4 inches (630mm) apart. The sheetrock installs over the plate, and the plate provides a template for a blind cutout of the hole in the sheetrock. The ceiling material is generally cut with a router-type cutting tool, using the plate ring as a cutout guide
For use with the EVID C8.2 and C8.2LP. Package of 4.
Installation_Instructions_94365_File_1.pdf
Electro-Voice Rough-In Mounting Plate - For C8.2 & C8.2LP Speakers - Pack of 4 (Electro-Voice RR-82-B) 
Service was great! Got a response to my question within 24 hours (next business day).
Customer support assisted me with a quest about rated amperage and this being a tax exempt purchase. Very helpful.
checkout was messy - shipping pricy...