Shafts and hubs are traditionally coupled by a key and a keyway. However, this method has many problems, including the need for higher quality materials, higher precision in machining, and positioning during assembly. ETP bushings provide coupling by means of friction as a way to resolve such problems. ETP bushings are products that use friction to couple without use of keys, which solves the shortcomings and difficulties of key couplings all at once. They have two primary mechanisms, hydraulic and mechanical (wedged). Their advantages are that they are simple, compact, lightweight, easy to mount and remove, and easy to position and index accurately. This greatly reduces work from the design stage to assembly, calibration, and maintenance.