Which type of gear is characterized by angled teeth and allows for the change of shaft direction?

Bevel gears are specifically designed with angled teeth that enable the transfer of motion between two shafts that are not parallel, typically at a right angle. This unique design allows them to change the direction of rotational motion efficiently. The angled teeth on bevel gears provide a greater surface area for contact, leading to smoother and quieter operation compared to other gear types.

In contrast, helical gears have teeth that are angled but are primarily used to transmit power between parallel shafts, not for direction change. Spur gears feature straight teeth and are used primarily for transmitting motion between parallel shafts as well. Worm gears, while they can change direction as well, primarily work as a gear reduction system and have a very distinct screw-like design, which does not involve angled teeth in the same way as bevel gears. Therefore, the defining characteristics of bevel gears make them the correct choice for this question.