8 New American Double End Clock Keys. This is a new set of 8 double end keys for winding clocks. Each key is steel, plated with nickel. The sizes are: Size 4, the small hole measures 1.75 mm and the large hole measures 3.25 mm. Size 4A, the small hole measures 1.95 mm and the large hole measures 3.25 mm. Size 5, the small hole measures 1.75 mm and the large hole measures 3.5 mm. Size 5A, the small hole measures 1.95 mm and the large hole measures 3.5 mm. Size 6, the small hole measures 1.75 mm and the large hole measures 3.75 mm. Size 7, the small hole measures 1.75 mm and the large hole measures 4 mm. Size 7A, the small hole measures 1.95 mm and the large hole measures 4 mm. Size 8, the small hole measures 1.75 mm and the large hole measures 4.25 mm.