Engine Mount
From Unofficial Stationeers Wiki
An Engine Mount is the first thing you have to add to the Launch Mount during the construction of a rocket.
You can build it using any of Kit (Fuselage Type A), Kit (Fuselage Type B), Kit (Fuselage Type C), Kit (Fuselage Type D).
You will need to attach an engine (one of Pressure Fed Gas Engine, Pumped Gas Engine, Pressure Fed Liquid Engine, or Pumped Liquid Engine ). Other Fuselage segments can be stacked on top.
Engine mounts A1, A2, A3, and A4 built from a Kit (Fueselage Type A)
Engine mounts B1, B2, B3, and B4 built from a Kit (Fueselage Type B)
Engine mounts C1, C2, C3, and C4 built from a Kit (Fueselage Type C)
Engine mounts D1, D2, D3, and D4 built from a Kit (Fueselage Type D)