The overcheck gag is a very tiny and neat bit popular with driving horses, and has holes in the loose ring cheeks to accept a very fine gag cheek. The gag cheek is a type of extended cheek piece that passes through the holes in the gag bit, with a ring at the base for the reins to fasten to, as opposed to the cheek pieces attaching directly to the bit ring as usual. Gags work by raising the bit up in the horses mouth, as well as poll pressure. The effect is usually to lift the horses head up in most cases. The overcheck gag is a strong bit designed to be used as a secondary bit, and need to be used with care as there is no limit to the amount the thin mouthpiece can be raised in the mouth.