Generally, a hand-buffed and polished bit indicates craftsmanship. Both sides of a bit must match in size and angles. Today most bits are made of stainless steel, fabricated in North America, Germany, England, or Korea. What matters to the horse is the material in the mouthpiece-metal, or metal covered with rubber or a tough nylon. A horse could resist a bad-tasting bit, although even the experts aren't sure what horses prefer.
Copper is a popular option, as it tends to increase the horse's salivation.
Stubbs noted that with less salivation, the horse is more likely to suffer from mouth pain. He added that a horse with a sore tongue might drink less water, as water washes away the saliva and the tongue hurts more. In the summer, a sore-tongued horse can dehydrate and possibly colic due to not drinking enough water. A bit's heft and weight affect its balance. The bit should rest comfortably in the horse's mouth, whether the reins are slack or taut with gentle contact.