Vanity Light Slotted Crossbar Adapter
A 120 x 22 x 7 mm crossbar that lets a new vanity or sconce light bar fit an old electrical box. The 4.5 mm end slots reach box-ear screws spaced anywhere from 64 to 96 mm apart, which covers both the 2-3/4 in and 3-1/2 in patterns. The 52 mm centre slot has an M4 hex-nut track on the back, so the fixture's two screws can land at any spacing from 0 to 52 mm and you don't have to drill into the drywall.
bathroom vanity-light electrical-box crossbar