Arcane University: Nifskope Prismatic Constraints
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Prismatic constraints allow a rigidbody to slide along a fixed line between two points. They are sometimes called rail constraints in other engines as they are alike a train moving along a rail. The prismatic constraints used by the Creation Engine optionally allow the sliding rigidbody to rotate about as it slides, though it is more common to use a fixed rotation.
https://i.imgur.com/5zrFQB0.gif (TODO get this uploaded. I don't have permissions I think)