This is a replacement REDS Engines Piston Pin. This part is compatible with the REDS R5, R5C, R5T and R5TE engines. The Piston Pin (wrist pin) is installed through the piston and into the upper rod bushing and connects the rod to the piston. When you remove the wrist pin, it is recommended that you install new wrist pin clips to prevent possible failure caused by using used clips.