Cleats connect to the bottom of a bike shoe that is designed for clip in pedals. Cleats can be screwed into the bike shoe so that a rider can connect his feet securely into a clip in pedal. The purpose of this is to increase pedalling efficiency resulting in higher speeds. Cleats are only used for clip in pedals which are most commonly found on road bikes, some mountain bikes and some BMX bikes. Cleats are extremely useful for their designed purpose but pointless to have if you don’t have the proper shoes or clip in pedals. Purchasing good quality cleats is advised as features such as quick-release are important when the need to unclip arises.