Bultaco exhaust nut typically used on Alpina’s along with many other models. The original exhaust nut typically takes a lot of abuse over the years. Renew yours with one that is tougher than the original and looks great. This exhaust nut is made of 304 stainless steel because of the tendency of the original nuts chrome to peel and rust. Size is 56mm x 1.50 which will fit your original cylinder. An oversized exhaust nut is available 58mm x 1.50 which would require you to chase the threads with a tap of the same size. Price $65 plus shipping for standard 56mm and $75 for the 58mm. Email or PayPal to mrgt350@yahoo.com if interested.