The antiquated Registered Jack standard is RJ45S, which always gets butchered to RJ45 in common parlance [and this sans-S version has never actually existed].

The antiquated Registered Jack standard is RJ45S, which always gets butchered to RJ45 in common parlance [and this sans-S version has never actually existed]. For RJ standards, an S suffix signifies that it is a "single line" circuit. https://en.wikipedia.org/wiki/Registered_jack#Types https://en.wikipedia.org/wiki/Registered_jack#Types https://en.wikipedia.org/wiki/Registered_jack#RJ45S https://en.wikipedia.org/wiki/Registered_jack#RJ45S