This is why I did this post, to settle in the minds of future fettlers. I added no text to the series of pics but instead linked the post to a very good thread where the 5 click system had been debated. Thanks for your positive remarks. Bill, its funny you should say that about a 71. I have one where the tank to burner threads are pretty poor. Its either a chop job or try and get the threads cleaned up. After reading the Whitworth Thread "thread" it looks like there is no way I would be able to get a tap and die to do the job!!