<p>How to measure a horse’s mouth There are various bit-sizer tools on the market to help you determine the correct size bit. This is an inexpensive plastic measuring device that slides into the horse’s mouth and shows you what size should fit – always go up a size if it falls between two. Some bit gauges also have a nylon strap so you can slip it over the horse’s head giving a more accurate measurement according to bit height. Check out if you have one of these on your yard, as they are quite hard to come by in online tack shops. Various manufacturers supply their own bit gauges to relate to their own bits. If you don’t have a bit sizer to hand and your horse will allow it, you can use a piece of string and a marker, marking the sides of the mouth and measuring the distance between each mark. Bits in the UK are usually measured in inches. However, Tricia cautions that as bit designs and thicknesses vary, that affects how they fit inside the horse’s mouth, so the measurement may not tally precisely with the right bit size. “It’s no good saying, ‘my horse is a 5.5in’, because some bits have more curve and fit differently, so you need to be open-minded to acknowledge what is in front of you,” she says. Measuring the mouthpiece So you know what size bit your horse should take, now to check the bit’s size. If you buy it new from a shop, this should be straightforward as it will be labelled. However, many of us have a box of bits in our tack room ready for whichever horse needs something different. It’s bad practice hygiene-wise to share bits around the yard, so make sure you have sterilised it first. You can put them in the dishwasher or soak in a home-made solution of water, vinegar, and baking soda, scrub and rinse. To measure your bit, first find a ruler (better than a floppy tape measure) and lay the bit flat on a hard surface on top of the ruler. The length of the bit is the distance from the inside of one bit ring to the other. For a loose-ring bit, measure from the inside of the hole for the ring. UK bits are measured in inches, and will be in the region of the 5in mark. You cannot go by the old adage for 4.5in for a pony, 5in for a horse, 5.5in for a draft horse – mouth sizes and shapes vary far too much for that. You will also want to know the thickness of the mouthpiece, as this can vary from around 12mm to as much as 23mm. “The easiest way to measure the thickness is with a digital caliper gauge,” suggests Tricia. “If not, put the bit on a ruler on a hard surface and measure in millimetres from above to get the diameter. If the bit is tapered, measure the widest bit next to the cheek. Twelve to 14mm is very fine, 16mm is the most common, while 20mm is very generous – more common on a mullen mouth or a rubber mouthpiece.” You may also need to measure the ring size. This is taken across the diameter from the inside of the ring to inside. A normal loose-ring snaffle would be between 60–70mm; a bradoon around 50–55mm, while 45mm is very small. Curb chains are simply measured from one end to the other, and tend to come in sizes small, medium and large. Finding the right size is not as simple as picking a bit off a peg. As well as being diligent about checking the size, you also need to be adept at switching from imperial to metric to general sizing. But for your horse’s sake, it’s worth taking a bit of time to get right.</p>