There is a big difference between practicing the holding the reins for a double bridle and learning how to use it (bits have different actions).To learn how to hold divided reins you can simply put two reins on a snaffle.
Then there is the intention of specific reinholds (of which there are 8). The main ones are:
The normal rein hold for 2:2 (two reins in each hand) is snaffle under pinkie, and curb between pinkie and ring finger. But for a horse just starting out in a curb the better use is 3:1 (both curbs and one snaffle in one hand (held slightly closer to withers) and one snaffle in the other), this allows the horse to 'settle in' to the connection. There is also 2:2 fillis/schultheis method which is snaffle over the pointer finger, and curb under pinkie; this method allows clear division of the aids.
And there is 4:1 for riding in one hand (hand over withers). For specifics look in books like Podhajsky.
Also one must really understand the 5 rein effects clearly (in a snaffle).
The use of the snaffle is for clearer hh/keeping horse up and open/allowing for chewing forward/down/out into a stretch. The use of curb is for lowering or slightly closing. Very distinct impacts upon the horse. It is said that the snaffle acts on the muscles and the curb onto the skeleton...not sure that I agree.
The most important thing is know what our own actions create in the horse's reactions.
For sure the use of a double is not to bit the horse stronger, and certainly never to hold a curb steadily torqued (to 45 degrees and beyond as we frequently see in pix of 'winners'). A big part is to properly fit a curb chain properly (not dangling loose, but to provent a torqueing of the curb).
Imho the best curb is a sliding cheek curb which allows it to move as the horse chews/tastes the bit.
Last edited by equitate; 01-22-2013 at 02:39 PM.