Magenis Loose Ring with Copper Rollers Bit Copper rollers help horses that pull to better accept the bit. Made of fine hand-polished stainless steel with copper rollers. Copper also encourages horse to salivate. This bit features 3 inch rings and a 14 mm mouth. All our Bits are High Quality Stainless made by Coronet. Mouth Size: 5, 5 1/2.