Moving the rein between the main ring and bottom ring allows leverage. Sweet iron and copper encourages the horse to be softer in the mouth. The 5" and smaller sizes of this bit have smaller rings to ensure the bit remains in proportion. Mouthpiece thickness: 16mm. Cheek height: 115mm (4.5?, 5?), 145mm (5.5?, 6?).
Stainless steel is the most common material for bits. Durable, easy to clean, tasteless and it does not rust.
Sweet iron mouthpieces are designed to oxidize to produce a sweet taste which helps with mouthing. Copper ribs and inserts will encourage mouthing but also ensure the horse will not take up too much of a contact, ideal for horses that can take a hold.