So, I want to get a D ring snaffle for helping to start one horse and switch a green horse to. But I am totally confused about which one to get. What‘s the difference between copper inlay, sweet iron, and regular? And square, twisted, and smooth, do I need to start with the softest snaffle-smooth(I think I do)? Thanks for future help, and please NO rude comments.
Get a thick, jointed, smooth D-ring snaffle. I see no reason to mess with anything else, at least not until your horses are much more advanced.
The stock cold air system is best until you swap the turbo to something bigger. As far as cat backs go, it's just up to you and which look and sound you like. If it's a 3 system, which is pretty standard, they all perform pretty close to each other.
Howard is right. Unless you get into major modifications, your stock system will suit you best.
The simplest is a wide jointed d-ring, the copper just encourages the horse to mouth up or salivate, though they will do this with a normal bit anyway. Twisted bits are too harsh and should not be used on a green horse that is being schooled. Always keep it simple when starting a horse. An eggbutt snaffle would also suffice.
Do not get square or twisted, these bits should never be used on any horse, there is no reason a horse needs them. Copper and sweet iron are meant to encourage salivation, salivation means more chewing, which means more movement in the jaw and ends with a suppler jaw. While helping you to have a softer mouth to work with copper and sweet iron are also prone to rust. So a smooth metal D ring is what you want. You should check both of the horses mouths before decided on lengths and widths. Make sure they have the same size and shaped mouth if you are using this on two horses. While thicker bars are softer on the mouth if the horse has a shallow pallet or a large tongue (or both!) it may be very uncomfortable for them.