Bar magnets are usually used for humbucking pickups and it eliminates 6 separate poles. Bar magnets have always been used for Gibson style pickups, though occasionally Gibson used rod magnets in some of their pickup/pickguard assemblies and P-90 style single coil pickups. Bar magnets have been used in many of Seymour Duncan pickups and have been used in Gibson Melody Maker, Firebird, Thunderbird Bass and several other models as pole pieces rather than adjustable screw pole pieces.