This part is a kind of semiconductor called SF56.

Function of this product has GLASS PASSIVATED SUPER FAST RECTIFIER.

Manufacturers : GOOD-ARK Electronics

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Some of the text within the PDF file :

SF51 THRU SF56 GLASS PASSIVATED SUPER FAST RECTIFIER Reverse Voltage - 50 to 600 Volts Forward Current - 5.0 Amperes Features High reliability Low leakage Low forward voltage High current capability Super fast switching speed High surge capability Good for switching mode circuit Glass passivated junction Mechanical Data Case: Molded plastic Epoxy: UL94V-0 rate flame retardant Lead: MIL-STD-202E method 208C guaranteed Mounting Position: Any Weight: 0.042 ounce, 1.195 grams DIM ENSIONS DIM A B C D inches Min. 0.283 0.189 0.048 1.000 Max. 0.374 0.208 0.051 Min. 7.20 4.80 1.20 25.40 mm Max. 9.50 5.30 1.30 Note Maximum Ratings and Electrical Characteristics Ratings at 25 ambient temperature unless otherwise specified. Single phase, half wave, 60Hz, resistive or inductive load. For capacitive [ ... ]

SF56 PDF Datasheet Download