Chuck (12) is formed in screwdriver shaft (10). Slot (14) in shaft (10) intersects chuck (12). Lever (16) is pivotally mounted in slot (14). Spring (24) biases the lever's tab (37) into chuck (12). Bit (28) has a collar (34) of length equalling the difference between the distance from pivot point (18) to (i) the tab's rearward face (38), and (ii) the chuck's rearward end. As bit (28) enters chuck (12), the bit's rearward end slides under lever (16), overcoming the spring's bias and pivoting the lever into a bit insert/release position. When the collar's forward face (36) moves rearwardly of rearward face (38), spring (24) pivots lever (16) into a closed position in which tab (37) protrudes into the chuck's rearward end, latching the tab's rearward face (38) against the collar's forward face (36), preventing unintended withdrawal of the bit from the chuck.