There are various measurements to consider when sourcing and assessing the correct size of bit including length, thickness, ring size and design.
Loose Ring Cheeks
The picture below demonstrates a popular loose ring snaffle bit, the Neue Schule Team Up. Other cheeks that are measured this way include the Universal, Beval, Balding Gag and the measurements to consider are here:
1) Mouthpiece Length: The measurement is taken by placing the bit on a flat surface and pulling the rings apart so the bit is at its maximum length. The Measurement is taken along the full length of the mouthpiece from the inside edge of the loose ring to the inside edge of the opposite loose ring and can be measured in inches or centimetres.
2) Mouthpiece thickness: This measurement is taken at the widest part near to the cheek just before the hole that the ring slides through. Again, if you put the bit on a flat surface , you can slide a tape measure below this point and, if you look from above, you can see the thickness. The most accurate way to measure the thickness of your bit is using an set of callipers, which are widely available.
3) Loose Ring Diameter: This measurement is taken from inner edge of the loose ring and is generally measured in millimetres; 70mm being the average for the standard loose ring bit; 55mm is the typical bridoon ring size.
Fixed cheek bits include the Baucher or Hanging Cheek, Full Cheek, D Ring, Eggbutt, Cheltenham Gag, and Nelson Gag. The picture below, showing the NS Tranz Full Cheek bit, is a good example of the points to measure at for this type of horse bit. As you can see, the only difference is that the mouthpiece thickness of the Fixed Cheek bit is measured directly adjacent to the cheek.
When sourcing a Weymouth for your horse, there are a couple of additional measurements to consider as demonstrated in the picture.
1) Shank length (lower): This measurement is taken from below the mouthpiece to the bottom of the shank (not the bottom of the loose ring) and is generally done in centimetres; 5cm, 7cm and 9cm are the options available within the Neue Schule collection.
2) Shank length (upper): In the Neue Schule collection this measurement has been scaled according to the lower shank length of the Weymouth.
Neue Schule mouthpieces are available in a range of sizes between 4″ (101 mm) and 6 1/2″ (165 mm). The table below shows the imperial/metric conversions.
Mouthpiece thickness varies according to the following table:
Cheek measurements vary dependent on cheek style and requirement, the table below shows the various options.