Broan Exhaust Fan 503/5 (B UNITS) 1.5A, Stack = 1-3/8" Shaft = .2178" X 1-1/4" 120V, 2 Spd 502,503,504,505,508,509, 510,511,512 UTILITY FANS * note old style units had a 2 hole mounted grille - new style has centre knob mounted grille - new style is identified with a “B” suffix Broan motor models 503/5 incl B