[teamtestbot]

Hey,

Most lower end and "common" drill gearboxes are 36:1, 9 tooth pinion, 18 tooth planets, and 45 tooth rings. This is the case with drills from Harbor Freight, Homier, and lower voltage Black & Decker and Ryobi. The reduction is (1 + R/P), so two stages of 6:1.

Those drill parts tend to be interchangeable, e.g. a B&D 9.6v will fit on the back of a Harbor Freight transmission.