Also known as geared spanners, a gear ratchet spanner can either be one-way or reversible. One-way gear ratchet spanners only go one direction. To change direction, you will need to turn the gear ratchet spanner manually. Although it depends on the capacity and size, one-way wrenches provide limited torque or pressure. However, they are a great place to start, especially if you are looking to add spanners to your toolbox.
As for reversible gear ratchet spanners, the name says it all. There is a lever at the bottom of the head. Pushing the bar will let you change the wrench in the other direction. It is more convenient than one-way spanners, but they do cost more. Choosing between one-way and reversible gear ratchet spanners can depend on your budget, as well as your requirements.
Just like spanners, these spanners are useful in tightening and loosening nuts and bolts. They come in metric and standard sizes. Check out our gear ratchet spanners here at The Grit.