BB-6 bottom brackets for 3-inch track, outside hookup, 11 gauge steel with a drilled pin. Same concept as the BB-5 but sized for 3-inch commercial track instead of 2-inch. Outside hookup means the cable routes on the outside of the bracket for low headroom setups where there is no room for a standard cable path. Sold as a matched pair. If you are working on a commercial door with 3-inch track and tight headroom, These springs are the right brackets. Confirm your track size first since 2-inch and 3-inch look similar but do not interchange.