Dr.D (7305 NS-4 Stainless Steel/Aluminum Slip-On Exhaust for Yamaha YZ250F The most popular exhaust in the DR.D line up. The DR.D SS/AL( Stainless Steel Tubing/Aluminum Can) is the exhaust chosen by more magazine test riders than any other; those who can ride with anything they want, choose DR.D. Lighter than the stock exhaust, the SS/AL features durable 304 Stainless Steel, TIG-welded construction and billet aluminum mounting directly on muffler can. Uniquely track tested to improve hit, delivery, and pulling power with substantial performance gains while reducing weight over the stock system. Welded construction, magnesium End Cap, removable bolts (not rivets) at the inlet cap for easy repacking, and stepped perforated core (reduced heat) for increased durability set DR.D apart in construction, and on the track.