Well when you think about a frame , say for a car or motorcycle , it ' s essentially just the shape and structural support . For instance , the only similarity between a street car and a race car of the same frame is just that the frame . Literally everything else is torn out and replaced with different equipment . In the case of an automotive frame you can get a lot of different ones due to different loads and aerodynamic design , etc . With Power Armor , however , there has to be a human inside , which severely restricts the design . Now , in game vs . lore terms there may very well be different frames , ones that use different hydraulics or wiring , but they can all support any armor piece because the shape is constant . What you as a player do when you fit that piece to the frame can really involve any amount of retrofitting and janky jankening . Compatibility is pretty much trivial since you can just rip out and replace whatever systems inhibit a different piece . It ' s essentially like fitting a 1970 era car with modern equipment . Totally doable since the frame is , after all , still in the shape of a car and built to support roughly the same thing even if it no longer uses a Carburetor or you swap out the manual transmission for an automatic .