"Coding" refers to the raised key on the connector.
A Code connectors have one raised key on the male connector and one mating slot on the female connector.  This is the standard coding generally used for standard sensor and distribution box applications.
B Code connectors have one raises key on the female connector and one mating slot on the male connector.  These are also called reverse keyed connectors and are used for some field bus applications.
Please select which coding type you need.