Crank noseband or Swedish Cavesson: used most often on dressage horses at levels where a double bridle is worn, this noseband is similar to the plain cavesson except it has a leveraged buckle design that may be adjusted very tight, so as to keep the horse's mouth closed. Double bridles cannot use flash or drop cavessons, so the crank is usually seen on upper level dressage horses who will not keep the mouth shut. It is also used occasionally on show hunters and hunt seat equitation horses. If adjusted so the horse can't open its jaw at all when the crank is tight, the horse also cannot relax its jaw. Additionally, it can push the cheeks against the horse's teeth when overtightened, which is painful. (source)