Thank you Eng, for your initial assessment, and thank you Wurger for your confirmation, and for the excellent pictures that show the placement of the various parts. Now we (the museum) know the correct terminology of the part ("hydraulic operating cylinder"; forget "coupler"). We have a Rolls-Royce Merlin engine, and a Spitfire prop hub (but it's 3-blade). I'm not sure how this display will come together, but you have helped us a lot with added knowledge about the parts we have. This is indeed a wonderful website, populated by wonderful, knowledgeable people.