This Kanstul model 33-S professional BBb tuba, with serial # 45090, has a 19-5/16″ bell, .656″1st-3rd, .689″ 4th, .710″5th valve graduated bore, is silver-plated, with SKB hard case. At last, a really-professional-grade 5-valve BBb tuba, made in the USA, based on the legendary York model 33 BBb tuba. The hand-lapped monel pistons have nylon valve guides for quiet, smooth operation, and the 5th valve is a patented Kanstul Controlled-Resistance rotor, a larger version of the rotors found on their professional trombones. The Controlled-Resistance design makes the response more consistent and even in the low register. The instrument is the best of classic York, plus improvements, all in a new instrument.