As mentioned earlier in the criteria section, mountain biking shoes use a 2 cleat mount and road cycling shoes require a 3 cleat mount. In the latter system, the cleat attaches your shoe to 3 bolts. These tend to be more stable on the pedal than their 2 bolt counterparts. On the other hand, the 2 cleat mount attaches your shoe to 2 bolts. These are simpler to clip-in and smaller, thereby making it easier to walk in. The 2 hole system is called the Shimano Pedaling Dynamics(SPD) system, whereas the 3 hole system is named after the first manufacturer of such a system: look-style system.