Measure Your Horse's Mouth for Proper Bit Sizing
Use this handy tool to measure the width of your horse's mouth for proper bit sizing.
By Suzanne Vlietstra

Is your snaffle bit the right width for your horse? Use this handy tool to check and see. Photo by Darrell Dodds

In the September 2006 issue of Horse & Rider, magazine Bob Avila shares his wisdom on bits ("Bob Avila's Winning Insights: Bits From Start to Finish.") Whether you're looking for a bit for a green horse or a veteran campaigner, you want to be sure you're selecting the right size for your horse's mouth. If your snaffle bit's mouthpiece is too wide or too narrow for your horse's mouth, the bit can't do its job effectively. Here's how to make a tool to measure the width of your horse's mouth--and how to use it as a guide to proper bit fit.

(Note: The measurement you get from this method isn't absolute, it's simply a guide to help you pick the correct mouthpiece for your horse. Standard width is 5 inches. Generally, horses with small muzzles and jaws wear a 4 1/2-inch mouthpiece, as a 5-inch model may look sloppy. Horses with larger muzzles and jaws are usually more comfortable in 5 1/2- or 6-inch mouthpieces, so the bit won't fit the corners of their mouths.)

You'll Need: An 8-inch section of 1/2-inch hose; a ruler; a pocketknife or leather punch; two rolls of different-colored, 1/2-inch wide electrical tape (we'll use red and yellow for ease of description); two split key rings; a lightweight headstall; two swivel snaps (optional).

Making the Measuring Tool
1. Using the ruler, mark points 1/2, 1, and 1 1/2 inches from each hose end. (The space between the two 1 1/2-inch marks should be 5 inches.)

2. Wrap a strip of red tape between the 1/2- and 1 inch marks at each end. Then wrap a strip of yellow tape between the 1- and 1 1/2-inch marks. Looking at the hose from left to right, you'll see 1/2-inch of bare hose, then a red piece of tape, then a yellow piece, then 5 inches of bare hose, followed by yellow tape, red tape and 1/2-inch of bare hose.

3. Using a pocketknife or leather punch, pierce a small hole in the hose end about 1/4-inch from each end. Then thread a split key ring through each hole.

4. Secure the rings to your headstall's cheekpieces, as though you're putting on a bit. Or, fasten swivel snaps to your headstall's cheekpieces. Then clasp the snaps to the key rings. (The latter is a bit faster.)

Mouth Measuring
1. To measure the width of your horse's mouth, bridle him with the measuring tool attached to the headstall, placing the hose in his mouth just like a bit. (Note: adjust your headstall so that the hose lies flat in your horse's mouth.)

2. The colored tape markers with tell you at a glance what size mouthpiece your horse needs. If the corners of his mouth are within the standard 5-inch width (the corners of his mouth are within the bare hose area) a 5-inch mouthpiece may be fine. However, when it comes to snaffle mouthpieces, wider is often better. Try a 5 1/2-inch mouthpiece; you may find him more comfortable and responsive.

3. If there's a gap of 1 inch or more between the corners of his mouth and the edge of the yellow tape marker, try a 4 1/2- inch or 5-inch mouthpiece.

4. On the other hand, if the corners of his mouth spread on to the yellow tape marker, opt for a 5 1/2-inch mouthpiece.

5. If his mouth spreads on to the red (or farthest) tape marker, a 6-inch mouthpiece may be best.

Suzanne Vlietstra is president of Hobby Horse Clothing Company, Inc., in Chino, Calif.