Bike pedals without locks, often referred to as "platform" or "classic" pedals, are a type of pedal where the cyclist's foot is not firmly connected to the pedal. The foot is simply placed on the pedal and held in place by the pressure and friction of the sole against the pedal surface. This design allows the foot to be removed from the pedal immediately and effortlessly at any time, which is particularly practical for city riding where frequent stops are necessary or for recreational cyclists. No special cycling shoes are required for riding, and they can be ridden in virtually any regular shoes. The surface of these pedals is usually designed to provide support and prevent the shoe from slipping. In basic models, it may be plastic with lugs, while more advanced versions, for example for mountain bikes, often have a metal body and are fitted with replaceable metal pins, known as 'pins', which dig into the sole of the shoe and increase grip. Unlike tread systems, where a special stop on the shoe "clicks" into a mechanism in the pedal, there is no such connection.