CRL Metal and Plastic Shelf Supports are intended to be used in glass or wood drilled hole panels. Drilled holes in panels are to be 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. Gray Rubber Cushions to protect the glass are sold separately. CRL steel plated shelf supports are sold 100 per box.