Hvac service wrench set are metal, strong, and resistant. the bit adapter is heat-treated black coating Bit Adapter: 2 inch long, size: 3/16'' and 5/16 There are 3 types you can choose, 1 set curved ratchet wrench, 1 set straight ratchet wrench and 1 Hexagon Bit Adapter 4 Different Sizes of Refrigeration Service Wrench Set: 1/4", 3/8", 3/16", 5/16", these sizes are the most commonly used sizes when repairing the air conditonning and refrigeration equipment Designed for repair use, for air condition, refrigeration and other equipments needing repair and fixing; for opening and closing compressor service valves, rotalock val ves and shutoff val ves, Manufacturer: Whoasyst