Type W Grating (Welded) – Most economical type, these grates are created by forge welding bearing bars and crossbars. Type SL Grating (Swage Locked) – Uses hollow tube crossbars that go through pre-punched holes in the bearing bars. Type DT Grating (Dovetail Pressure Locked) – Using an “egg crate” configuration, these grates have crossbars that fit vertically into slots in the bearing bars.