The 9155013 Nickel / 9155013B Black is a Three-Module Flush-mount Frame for use with 9155016 flush mount box.
The 9155016 Flush mounted box for walls or plasterboard for 1 module is for use with 9155013 Flush Mount Frame. The box cannot be used for surface installation.
Price quoted below includes Flush Mount Frame + Flush Mounting box.