Features Key of Bb/F double .468" bore 12-1/4" diameter, hand-hammered, yellow brass bell Large throat. Description Product Description The H378 is made of yellow brass, which produces a higher tone color with more overtones for clearer projection. It is capable of playing pianissimo staccato notes clearly and evenly. Key of Bb/F double; .468" bore; 12-1/4" hand-hammered, yellow brass bell; large throat; .310 venturi of yellow brass; noiseless string action, short stroke with stainless steel springs; tapered hand-lapped rotors; nickel silver slides inside and out; lacquered brass finish.