XT60U-F :  High-amp secure battery connector for R/C. Upgraded version of the XT60 connector. For this new XT60U series, the "-F" means female; this connector is typically on the battery pack. Used for Receiver and Motor applications. This XT60U connector is differentiated from the traditional XT60 connector by having a semi-circular NEG (-) terminal, as opposed to the beveled-edge terminal.