General Purpose Girths
A girth should first and foremost spread pressure evenly over the entire area. If it is too narrow it may cause discomfort. It is also best if it has some “give” to it, which makes it more comfortable for the horse. Many riders also choose a girth that allows for extra elbow room, so the horse is not restricted as his leg moves backward.For horses on which the saddle sits nicely, neither slipping forward or back, the first and third billets should be used. On horses where the saddle slips back, the first and second billets should be used. The second and third should never be used together, as they are attached to a single piece of webbing to the saddle’s tree. Since the first billet is attached to a separate piece of webbing, you can safely combine its use with either of the other two billets.
There are other girthing systems available such as the Adjustable Y system or a similar girthing system. These also provide an adjustment option and have a front girth strap which is connected to the saddle tree point, and a rear girth strap giving it a Y shape and stability.