The seat tube extender isn't in the build blog because the camera battery was flat on the day I made it. The tube is the seat tube cut from an old scrap 531 frame 28.6mm ext. dia and 27.2mm int. dia. It has a lug, made from 2mm steel plate, brazed-on to fit the 'Palk strut'. The strut is made from a seat stay cut from the same scrap frame. Seat post is an Isaac carbon 27.2mm item. The strut is essential with my saddle height (and weight!), to prevent the base of the extender tube failing.