Yes, some are prefabricated and they come in sizes ranging for double zero (00), zero (0), 1, 2, & 3, if I recall correctly. Possibly half sizes exist as well, but these are the common sizes available for purchase at many feed/tack stores. read more
Some people will say things like 'my horse takes a size 4 horseshoe', whereas in fact the horse takes size 4 of the brand of horseshoe that their farrier happens to be using, but with a different brand the horse may require a size more or a size less ( e.g. a size 3 or size 5). read more
Their entire weight comes down on their hoof and though shoes do protect the “nail” - the shell of the hoof — they don’t keep the weight of the horse coming down repeatedly on such a hard surface from damaging the ligaments and small fragile bones in the other parts of their legs. read more