This is the “Patent Bridle,” invented by Dennis Magner, a popular and prolific 19th century author on ‘scientific’ horse training. This illustration is from his 1886 “The Art of Taming and Educating the Horse.” This may be the earliest gag bit, at least of the strap style. Anyone know of (or suspect) an earlier one?
It is slightly different from modern gags in two effective way. First, the pulley gives a little bit more leverage (re: stronger upward pull) than a modern strap. And second, “a rubber connecting the ends of the bit to the rings on the pulley reins makes the action of the bit upon the mouth the same as any ordinary bit. But if at any time there should be much resistance, the rubbers stretch sufficiently to give play to the reins upon the pulleys.” If true, a very neat innovation, though I’m not a fan of gag bits, especially ones with as long a strap as this (a stopper could be added to prevent maximum engagement and the possibility of severe lip damage).