cant remember the bore, but i can rember those ready made pipes on the bay are about as usefull as a chocolate fire guard.. Avoid them mate. when i fitted mine, some members on here tried these pre made items and they did not fit right, custom bit is the way to go, let them re alighn your backbox too, we had to lob off a hanger on mine and re weld in a slight different location - coz i didnt have the fixing kit magnex supply when u get them new, this kit re locates the hanger point on the car its like a plate, mine arrived about 2 weeks after i got my exhaust fitted

, so i sold it on ebay and got £60 for it!!!
its not available to buy no more..
anyhow in a nutshell, go custom for your centre bit