CRL Metal and Plastic Shelf Supports are intended to be used in glass or wood drilled hole panels. Drill holes in panels 1/4" (6 mm) in diameter. Usually, the 1/4" (6 mm) holes are drilled 2" (50 mm) on-center in rows of 24 (48 total holes per panel). This insures that shelves can be easily repositioned and your display fixture has maximum flexibility.