This block works for Ruby Robot!
The Brake Wheel block allows to momentarily brake either one of the robot's two wheels, or both of them at the same time.
The default choice is "both", but you can easily change that by opening the drop-down menu and selecting "Right" or "Left" :
Braking VS Stopping
Using this block will not stop the robot in its tracks, but rather slow its speed for a fraction of a second. It is comparible to putting your foot down on the brake pedal of a car for a single second and then releasing: the car will not stop completely, but it will slow down for a moment.
If you want the robot to stop completely, better use a Brake Until Stop block!