According to Professor Hubert J. Farnsworth, the differences between the two robot sexes are "ill defined". The main difference between them being their type of oil, and apparent design of the robots to emulate the human sexes (i.e. fembots tend to have long eyelashes, higher voices, and a somewhat more feminine physique than manbots). For manbots, the interior of a fembot would be the same as a nude human woman for a human man.
An electrical diagram of a fembot, the robotic equivalent of pornography (1ACV05).