XT60U connectors are manufactured by Amass, and are upgraded versions of the classic XT60 connector. XT60U's are slightly smaller in dimension and slightly lighter weight, while still being backwards-compatible with the original XT60 design. XT60U's also claim to be good for a few extra amps due to higher quality contact elements. Color may vary--typically yellow or black.
Male (ESC side) connector
Made from the same high quality nylon as the original yellow XT60, these connectors can withstand up to 65A continuous without overheating, deforming or breaking apart. XT60 Connectors are manufactured from high-temperature nylon and are fitted with gold plated bullet connectors. The bullet connectors are fitted during the injection mold process to ensure a tight fit.