Boxes with concentric or eccentric knockouts are suitable for bonding without any additional bonding means where used in circuits above or below 250 VACUnless otherwise noted all concentric or eccentric knockouts are 1/2 to 3/4 in combinationsSingle and double gang metallic outlet and switch boxes are acceptable for use in two hr fire rated wallsGroundskeeper raised ground feature on boss inside box provides one or two #10-32 tapped hole, allowing a 3/8 in long green ground screw to be threaded into box without contacting mounting surfaceOther boxes provided with flat ground tapped hole, except plenum boxesSingle device2-3/4 in centre to centre open earsCeiling plaster rings/mud rings