Straight subs: Used to connect drill stem members that have a similar OD. Reduced-section sub: Used to connect drill stem members that have different diameters that warrant the cross-sectional change necessary to accommodate different connections. Saver sub: Used to extend the life of the rotary kelly by taking the connection wear each time it is made up to a drill stem component. Bit sub: Size availability ranges from 3 1/8 in to 11inch OD and 36in to 48in length. Lift sub: A lift sub enables the safe, efficient handling of straight OD tubular, such as drill collars, shock tools, jars, directional equipment, and other tools, by using the drill pipe elevators. Top drive sub: Top drive subs serve as the sacrificial element between the drill string and the top drive, reducing repair and maintenance costs.