Two basic designs, weld in and bolt in. The weld ins are going to be stronger but the bolt ins are more convenient(you can always weld in the bolt ons later if you want). As with everything else you get what you pay for. If you buy an expensive brand, chances are, they will fit better. If a vert there is a spacing issue with the cross-over brace that can also effect the exhaust system but there are work arounds for this. Check out Summit and Jegs for what's available and then shop around for the best price.