Been a while so I have come back to this project and finished off the gas supply (I think). I really have to get into 3d sketching before all this pipe work blow my mind. Just a turnbuckle to dream up now, but I'm really not clear what they look like.
Final part of the jigsaw - the turn buckle. Drawn using my vivid imagination - Rob/Paul do you think it looks ok?
Almost, there is/was usually a big nut on each outer end. Presumably one left hand and one right hand thread so that when twisted it tensioned the rods. No nuts in between. I will try to find a photo.