Thank you everyone. I was a bit too tired to search last night and I was going around in circles. Your comments have really helped, although I am still a little unsure, but I will try and get my head around it. I guess mine is the standard 1". I don't yet understand the terms on Sheldon Brown's chart but I will take Road Fans advice and study the whole site at the weekend. Thanks bigbossman I now understand the measurements refer to different things. Thanks Charles I took your advice and looked for old cinellis. You are right there are some nice ones out there; you may have saved me a lot of cash. Thanks again.