Rail Post

The Rail Post is a railway item in Astroneer. It allows for the creation of rail lines, and can be used to recall Rail Engines to it. It can also be used as an “extended Extender”, being able to channel power and O2 between bases.

Source
Rail Posts are placed from a.

Uses
Placing a Rail Post within range of another will connect a rail line between them, deforming any terrain that might be in the way.

Rail Posts may be placed on any terrain, allowing for placement on walls and ceilings of caves.

The maximum placement distance for the post is shown as a coloured dial on the base of the post when placing.
 * White indicates valid placement, below the maximum rail length.
 * Blue indicates valid placement at optimal rail length.
 * Pink indicates invalid placement -- whether from being placed too far, too close, or from creating too sharp of a turn.