Fitting - "B" Male Adapter - Fuel
This "B" fitting male adaptor is a left-hand thread used to connect fuel "B" fittings together.
Left hand threaded connections all have a mark around the hex nut to identify that it is a left-handed thread. To tighten these connections, the nut needs to be turned to the left (opposite of what most people are used to). This ensures that fuel connections stay with the fuel side of the torch and cannot be connected to the oxygen side of the system.
This is the industry standard for connecting 2 fuels “B” fittings together.