Twin Pillow Block Linear Ball Bearing IPPSW08G 1/2" Closed - Self Aligning Precision PlusTwin Linear Ball Bearing, closed shell, with a 1 2" ID (inner diameter) inside a housing made of aluminum alloy. It is self aligning due to a crowned bearing shell inside the housing. The IPPS products all come with a grease zerk fitting, a small hole in the pillow block which is also called a lubrication port. Twin bearings come with 2 lubrication ports. Twin Double size equal to two standard bearings mounted back to back Temperature Range: 4 +176F (