The April 29, 1924 patent is #1,492,095, issued to Samuel Duncan Black and Alonzo Galloway Decker (yes, the original Mr. Black and Mr. Decker). It covers the trigger-operated rotary switch that alternates between "On" and "Off" with each pull. So, you have to pull the trigger again in order to turn it off - really scary if the drill bit sticks, especially if you're using one of their bigger drills (5/8", 3/4" and larger)! Part of the purpose was to make it possible to swap out a burned-out switch without special tools; making the handle-and-trigger assembly including the cord exit detachable from the rest of the drill with just four screws helped accomplish this. Their original patent, #1,245,860 (Nov. 6, 1917) had the same alternating action switch, but wasn't readily changed out. It also claimed the pistol-grip handle centered beneath the drill's center of mass, and the enlarged area above the user's hand to more easily support the weight.
They also patented the reversing switch for electric drills in 1925, and the cord protector (that tapered sheath where the cord exits the handle or body of the drill) in 1926, so a lot of the features we take for granted were their inventions.
