B-17E/F Tail Wheel, Hayes G-3-217, Firestone K0-200-195 Pre-WW2 They could be opened inward

They could be opened inward to allow a pilot to de-ice his main windscreen or

This is a Horsepower Indicator

Typically mounted on the rear housing of a 50 cal machine gun from a side/waist gun position in the aircraft

See photos of the diagram and descriptive text from the B-50 Flight Manual

B-17E/F Tail Wheel, Hayes G-3-217, Firestone K0-200-195 Pre-WW2 They could be opened inwardWHEEL ASSEMBLY 26. 00 SMOOTH CONTOUR TAIL HAYES G 3 217, G 3 168 FIRESTONE K0 200 195 CHARACTERISTICS: Rim type drop center, Flange type . demountable Axle type stub Axle diameter .. inner: 3. 000 inches, outer: 2. 500 inches RELATIONSHIP OF PARTS: Used with: Tire diameter . .. 26 inches Flange diameter . 10. 500 inches Ledge diameter . 8. 250 inches Overall width 11. 200 inches Weight . . approximately 19. 25 lbs. (aluminum permanent mold) Casing 26.