The Weymouth should be a snug fit and you don’t need to see any of the mouthpiece. The lips should be allowed to spread naturally and brush up against the shank.
If you have a fixed cheek for a bridoon the fitting would be the same as above for the Weymouth and it is likely that both bits would be the same size.
If the bridoon is a loose ring there is normally a ¼” size larger than the fixed cheek Weymouth. This is because the general rule for a loose ring would be to have clearance either side of approximately one eighth of an inch from the corner of the lip up to the hole that the ring passes through.
A general guide to ensure your horse’s bridoon bit is at the correct height in the mouth would be to aim for ½ – 1 lip wrinkles at the corners of the mouth. Please bear in mind that mouth conformation varies, and some horses are much shorter from the corner of the lip to the muzzle (‘short smile’). In this case it is often tempting to shorten the cheek pieces excessively. However, this can create unnecessary pressure in the commissures of the lip, leading to discomfort, may predispose to rubs and masking of the rein aids.
The Weymouth should be positioned lower than the snaffle so that they do not interfere with each other. You can check this by placing your finger very carefully between them from the side.
When the curb chain is attached correctly it should restrict the shanks from rotating any further back than 45° in relation to the horse’s lips.
Some riders prefer to remove the traditional curb hooks from the weymouth and replace them with quick links. Riders with horses that often find that the curb chain or hook has rubbed the skin when in doubles have often found that swapping to quick links has been the solution.