When my Simonini exhaust arrived it had a separate flange that bolted to the engine and the exhaust had a wider diameter to fit over the top. It was supplied with two springs that were meant to hold there two parts together. The exhaust had two little hooks to attach the springs but the flange had nothing. I found out the hard way that not using the springs turned the exhaust into a projectile. Anyway I drilled a couple of holes in the bolt on flange so I had something to hook the springs on and it seems to work.