This is a basic replacement stainless steel arm for the Fender Contemporary System 3 tremolo used on MIJ Stratocasters, Telecasters and Squires that were made between 1985 and 1987.
The original arm is extremely hard to find, it had a screw on tip with built in allen keys on both ends. This basic version has a rounded tip and no allen keys.
The square cut end is used to turn the tremolo on or off by pointing the arm towards the ground.