“Besides the usual cargo lock we had three Kwikloks. A Kwiklok is an Iron Maiden without spikes; it fits a man in a suit, leaving just a few pints of air to scavenge, and cycles automatically. A big time saver in changing shifts. I passed through the middle-sized one; Tiny, of course, used the big one. Without hesitation the new man pulled himself into the small one.”
Delilah and the Space-Rigger by Robert Heinlein (1949)
Standard Sign for a Kwiklok
Version 2.
Kwikloks may be encountered on spacecraft or space habitats. They are airlocks intended to for the rapid passage of a single individual. Their small internal capacity allows them to be rapidly filled or emptied of air.
A typical kwiklok resembles a sarcophagus set in a wall. Each door has a window at face level in an attempt to counter the sensation of confinement when using a kwiklok.
Individuals taller than 78 inches will have difficulty using kwikloks. Obese individuals or those with exceptional bulk for other reasons may also find it impossible to use a kwiklok. Microgravity-adapted humanoids such as floaters may be up to a foot taller than baseline humans. Suitably proportioned kwikloks are common on microgravity habitats and may be in the majority. Observing the configuration of kwikloks present may give clues to the population within. 
The amount of equipment a normal-sized individual can take through a kwiklok is limited. The claustrophobic should avoid kwikloks!
A kwiklok designed for rapid cargo transfer has a capacity of about one cubic yard, and resembles a safe with a door on two sides. The floor is often constructed as a sliding pallet to facilitate loading and unloading.
Kwikloks of around one cubic foot capacity are used to pass items such as rock samples and tools between exterior and interior.
Kwikloks designed for the passage of robotic systems, octosaps (THS Under Pressure 3e p.101) or astropuses (THS 3e p.118, Bio-tech 3e p.104/ 4e p.91) may be encountered.
Kwikloks are also used on underwater habitats and vessels. Standing for the first time in a coffin-sized closet while it rapidly fills with water is a memorable experience!
Kwikloks are also found in research facilities where it is important that the interior of a room cannot be contaminated by the atmosphere of another. Such kwikloks may include decontamination systems.