Myler Medium Shank Narrow Medium Ported Barrel Bit Stainless Steel 6 3/4" MBL Medium Shank with Sweet Iron Medium Ported Barrel Narrow (MB 43MP, Level 2-3) Copper Inlay. This mouthpiece is made of polished Sweet Iron which naturally oxidizes or rusts. Harmless to horses, it has a sweet taste and promotes salivation.