This is a Futaba/KO battery to JR transmitter adapter. This adapter allows you to use virtually any transmitter battery to power your JR transmitter.
NOTE: Be careful when using JR car or KO car transmitter batteries, as the polarity is reversed on those packs. Make sure you change the polarity of one of the connectors by removing the pins and swapping them if you use one of those battery packs.
ProTek R/C is an A Main Hobbies brand.