To find the small size of a tapered bore, multiply the length of the taper by the taper size in inches and divide by 12 to get the ratio. Subtract the ratio from the biggest size of the taper to determine the small size. For example, with a taper length of 1.250 inches and taper size of .750 inches, the ratio is 0.0781 inches. Subtracting this from the biggest size of 3.123 inches gives the small size of the tapered bore as 3.045 inches.

1. How to find the small
size of a taper bore
Sometimes is necessary to find what size the bore
is going to be on the small size
Length of tapered bore X taper size (in inches)
divided by 12 = Ratio
Rest ratio to the biggest size of the taper
SF SK (letters) = .750
4545 2030 (numbers) = 1.67834
1.250 (length of tapered bore)
X .750 Ratio
0.9375 ÷ 12 = 0.0781
OD of SF GAGE
3.123 – 0.0781 = 3.045
This is the measure of the
small size of the bore