This king of bushing is the necessary product of driling rig. It matches with the master bushing to drive the kelly. This product rotates the kelly through four rollers to reduce the friction thus extend its working life. This product has square drive and pin drive two forms. It can match with different type of kelly by changing the rollers. It is designed and manufactured according the API SPEC 7K Standard, and have the certificate of authority to use the official API monogram.