I addressed this problem several years ago on this Forum based upon my experience with Armour pipes about ten years ago. I bought a set off them where all the tubes had the same diameter, including the ones at the front of the silencer and the short stub where the short pipe fits into the long pipe so there was no chance of ever fitting them together. When I phoned them up to tell them about this they told me that it was impossible until they went and checked and found that they had six identical sets on the shelf. The replacement set would also not fit but I did manage to make the third set fit. I had to cut the pipes to length and re-flange them. The hole in the long pipe to allow the gas from the rear pipe to enter the long pipe was a very roughly cut hole, about three quarters of an inch diameter, which I had to open up with a die grinder and a solid carbide bur. I like to try to make things better for the future and so I offered, entirely at my expense, to take a bike down there so that they could fit a pair and then make a jig to ensure that all future sets fit. I got an arrogant response to the effect that they did not need any help and they had a local Vincent owner available if they did. There is another common fault with Armour pipes and that is the position of where the short rear pipe joins the long front pipe. This joint should be about where the big end quill is but their pipes generally have this a long way too far forwards. It is a pity as, if you do not mind the appearance of stainless steel, they are a good price and will not rust. I am a great supporter of Bob Culver and the work he puts in to keeping our bikes going but I really do not understand why we are still messing about with this pipe bending technology. Anyone who has seen a modern, computer controlled pipe bending machine extruding pipe at feet per minute with each pipe identical to the other will understand why I ask that question.