17. The illustrated shaft has an overall length of 42 inches. If the diameter of «F» = 3.75″ and «X» = 6″, with an indicated radius of «R» = .125″ and a taper per foot, of «L» = 1.5″; then the small diameter «E» is __________

The small diameter 'E' is 2.500 inches. The taper of 1.5 inches per foot, combined with the 10-inch effective taper length (accounting for the fillet radius), results in a 1.25-inch reduction from the initial diameter of 3.75 inches.