Works with the following Dogtra Dog Training Collars: 202NCP (Serial Number less than 101961), 1802NC (Serial Number less than 100101), 1803NC (Serial Number less than 100101), 1804NC (Serial Number less than 100126), and EF-3000 Old. Need to purchase the primary splitter of 5-3 to expand off of. Yellow 3mm female and two yellow 3mm male connectors. Makure sure you know exactly which splitter you need before ordering