Bulkhead Endcaps and Viewports
These low prim bulkheads can be used to cap the ends of any corridors, junctions or other modules so that doors can open to extra features, such as rotating fans and viewing ports. Touching the striped area on the door frame will auto-align the unit to any other with a similar bulkhead door frame. Which means you can connect them with anything with a similar frame from Exosphere