Garrett Operational Test Piece (OTP) for Walk-Through Metal Detector Testing. The Operational Test Piece by Garrett is designed to mimic the size shape and composition of a forbidden object for testing and verifying calibration settings of walk-through metal detectors. The Garrett Operational Test Piece OTP 1600600 is made to meet the specifications of the Federal Aviation Administration (FAA). For more quality Metal Detector Accessories by Garrett please visit our Garrett Metal Detector Accessories page. Garrett Operational Test Piece (OTP) for Walk-Through Metal Detector Testing 1600600