Grundfos 18"" Steel Simplex Cover with 3"" Vent Specifications - Grundfos 18"" Steel Simplex Cover with 3"" Vent: • Standard Bolt Circle-Holes: 19-1/4 - 4 • Cover O.D.: 20-1/2"" • Pump Access O.D.: N/A • Discharge Size: 2"" • Inspection I.D.: N/A • Cover Thickness: 7 ga. • Requires bolt and gasket pack, sold separately."