Snaffle Bit: a simple jointed bit for a horse; without a curb
Leverage Bit: Bits that have shanks coming off the bit mouthpiece to create what is known as leverage
All horses should be started in a snaffle. They are the least harsh bit and give a horse an easy, direct message of what you want your horse to do. Snaffles are available in several variations including simple o-ring, full cheek, eggbutt, and d-ring, and normally I would start a horse in just a simple o-ring like this:
When using a bit like this your pull on the horse's mouth is equal to 1lb of pressure for every 1lb you pull. This mean you pull 3 lbs of pressure with your hand, the horse feels 3lbs of pressure. You pull 5lbs and your horse feels 5lbs of pressure. The best thing about this bit is there is just one clear concise message the horse feels and that is the pressure that you are pulling on their mouth. There is no poll pressure, no curb pressure, etc. like with other bits. I would always recommend using a snaffle bit to start a horse.
Now depending on what type of riding you plan to do, this is where you want to decide what type of bit you want to finish your horse in. I never recommend moving up from a snaffle until your horse is "trained." With my experiences this means Western and for this I would want my horse moving off pressures, neck reining, stopping with little force of the bit, walking, trotting, cantering, galloping, etc. Once I have accomplished all of this in a snaffle I would move my horse into a bit such as this:
This is what is known as a curb bit. Instead of hooking the bridle and reins to the same part as in the snaffle bit, we now connect the bridle to the purchase part of the bit, and the reins to the shank part of the bit. We will also use a curb strap on a bit like this. What this bit allows us to do is encourage a headset, use less power to cue our horse, and neck rein properly. A horse tends to be more responsive in this bit, but to an untrained horse it can be very confusing putting too many pressure points on the horse at once. A bit like this does several things. The most important one in my opinion though is the leverage pressure. While I told you before a snaffle bit puts 1lb of pressure on a horses mouth to every 1lb of pressure you use, a curb bit puts more pressure on a horses mouth. It's an easy calculation to figure out how much pressure your bit exerts. To do this you must know the difference between the purchase and shank.
The part above the mouthpiece is called the purchase, the part below the mouthpiece is referred to as the shank. The calculation for a curb bit's pressure is simple, shank:purchase. For example let's say you have a bit with an 8" shank and 2" purchase. This means you have a 8:2 pressure ratio meaning for every 1lb of pressure you pull the horse feels 4lbs of pressure. So now for example we used 3lbs and 5lbs of pressure with the snaffle bit. With a shank bit (8" shank, 2" purchase) a horse would feel 12lbs of pressure and 20 lbs of pressure rather than 3lbs and 5lbs. A shank bit can obviously get harsh extremely quick so it takes a well trained supple horse and a rider with soft hands to be able to successfully and safely use a bit like this! Now think of a harsh western bit with an 8" shank and 1" purchase. That doubles the pressure your horse feels, so instead of feeling 12lbs and 20lbs they now feel 24lbs and 40lbs of pressure. I tend to stick with a bit of no more than a 6" shank and 2" purchase.
There are many other factors that go into leverage bits as well. For example, a simple tom thumb bit looks like a snaffle bit with the mouthpiece and are oftentimes marketed this way as a good training bit for your horse. Instead a tom thumb bit can be extremely harsh to your horse! With the nutcracker action accompanied with the shank a tom thumb bit can pinch the inside of a horses mouth and cause severe pain. For this reason I recommend when using a leverage bit only to use ones with a solid mouthpiece or a jointed port in the center.
There are many factors that go into bits including how tight you have your chinstrap, how tall a port is in the mouth, what the design is of the curb, etc, but this should give you an idea of how harsh your bit you're using really is. Have a great ride!!
