Flat machined covers are made for pressures greater than basic yoke & bolt or vacuum clamp bolt manways can tolerate. These covers are available in standard thicknesses or in custom specified thicknesses that allow for a higher range of pressure / temperature conditions. Designed for use with yoke & bolt hardware. Covers are made of carbon steel (SA105 Forging, SA516gr70 PVQ Plate, Stainless Steel).