2-1/8 in electrical box is pre-mounted and centered on bracket and is fully adjustable up to 8 in either directionElectrical box has 3 open knockouts for quick installation(3) 1/2 in bottom, (4) 1/2 in side knockoutsNVent CADDY SPEED LINKâ„¢ to support from building structure and two fixture mount stabilizer clips (FMSBC1) to stabilize ceiling tiles