Slotted perforated metal is produced in ferrous materials in plates, stainless steel or galvanized steel. Oblong Slotted Perforated Metal: 3.175 x 25.400 mm oblong slot 6.350 mm centers Side Staggered 43% open 22 gauge steel Length of oblong slots run length of sheet. 1/4" Slotted Perforated Metal: 6.350 x 38.100 mm slot Every third bridge 4.763 mm wide Other bridges 2.381 mm 67% open area of sheets 16, 18, 20 gauge steel Length of slots runs width of perforated sheet.