The Universal Socket Interface (USI) was a non-proprietary standard for droid appendages, used since 322 BBY.

In 22 BBY, Cybot Galactica for the first time broke off with this standard by creating the Advanced Appendage Bus for its droids, which, according to the company's Chairman Illia Setag, "more than triples the data-flow which will allow advancements in sensory input, perhaps allowing advanced tactile functionality for droids and prosthetics in the near future".