Bit Sizing Guide
A bit that fits well helps your horse work in comfort. The right size protects the corners of the mouth and helps the rein aids reach your horse clearly. This guide explains how to measure your horse, how bit width and thickness work, and how to read cheek styles and materials. The Size option on each Sprenger and Nathe bit lists the widths available for that model.
How to measure your horse for a bit
1. Use a piece of soft string or a shoelace. Hold it in your horse's mouth at the spot where the bit will sit, with a finger marking each corner of the mouth.
2. Mark the string where it meets each corner, then measure the length between the two marks with a ruler.
3. Add 0.5 cm to 1 cm to this measurement. This gives you the bit width to look for.
4. If you already have a bit that seems to fit well, you can measure that instead. See "Check an existing bit" below.
How to check an existing bit
Do up the bridle as normal, then stand in front of your horse and gently pull the bit sideways at the rings.
On a loose-ring bit, a gap of 3 mm to 5 mm should show between the ring and the corner of the mouth, on each side. Both rings should turn freely without pinching.
On a bit with a fixed side piece, such as an eggbutt, D-ring, or full-cheek, the side piece should sit close against the corner of the mouth, without pressing into it.
Bit width chart
Bit width is the measurement across the mouthpiece, from the inside of one ring to the inside of the other. The chart below is a general starting point only. Always measure your own horse using the steps above, since mouth size varies between individual horses of the same type.
| BIT WIDTH (MM) | BIT WIDTH (INCHES) | TYPICAL HORSE TYPE |
|---|---|---|
| 95-100 mm | 3.74-3.94 in | Small pony (measure to confirm) |
| 105-110 mm | 4.13-4.33 in | Pony |
| 115-120 mm | 4.53-4.72 in | Cob |
| 125-135 mm | 4.92-5.31 in | Horse (Full) |
| 140-150 mm | 5.51-5.91 in | Large horse / Warmblood |
| 155-175 mm | 6.10-6.89 in | Draft horse / Extra-large horse |
Sprenger's pony sizes start at 105 mm; the 95 mm to 100 mm sizes suit only the smallest ponies.
Why there are no half sizes
Bit sizes go up in 1 cm steps of mouthpiece width. That is only a 5 mm change on each side of the mouth. A half size would be a 2.5 mm change on each side, which is within the normal range a horse's mouth can tolerate. If your horse falls between two sizes, try a bit with a fixed side piece instead of a loose ring. A fixed side piece sits closer to the corner of the mouth, and this can close the gap.
Bit thickness explained
Thickness is the measurement across the mouthpiece itself, not the width. Most horses today are ridden in a thickness of 14 mm to 16 mm. The average horse has only around 3.5 cm of space between the upper and lower jaw, and the tongue takes up 2 cm to 2.5 cm of that space, so there is often less room for a thick bit than riders expect.
Use the 2-finger test to check thickness. Place two fingers flat, one on top of the other, on the bar of the mouth where the bit sits, then let your horse gently close its front teeth. If you feel pressure on both fingers, choose a bit no thicker than 16 mm. If you feel no pressure, there may be room for a thicker bit.
Ring and cheek styles
A loose-ring bit has a mouthpiece that moves inside the rings. It suits a young horse, or a horse and rider still building a steady contact, since the moving ring softens an unsteady hand.
An eggbutt, D-ring, or full-cheek bit has a fixed side piece instead of a moving ring. It gives more sideways support in turns, and suits a horse that falls out through a shoulder, plays with a loose-ring bit, or has sensitive corners of the mouth. A bigger side piece gives more sideways support, so a full-cheek gives more support than a D-ring, and a D-ring gives more support than an eggbutt.
A weymouth (curb) bit is used with a double bridle. The bradoon sits on the rear cheekpiece, and the fixed weymouth mouthpiece sits on the front cheekpiece with a curb chain.
Bit materials explained
Stainless steel is the standard entry-level material. It has no taste or smell, and it wears well over many years.
Sensogan is a copper alloy containing copper, manganese, and zinc, with no nickel. It is designed to encourage a horse to chew and produce saliva, which helps the horse accept the bit. Sensogan developed from an earlier Sprenger alloy called Aurigan. Some current models still use Aurigan for the rings or cheeks, paired with a Sensogan mouthpiece.
Nathe bits are made from a smooth thermoplastic. They suit a horse with a sensitive mouth, since the smooth surface does not drag on the tongue the way a dry rubber bit can. Nathe mouthpieces measure 18 mm or 20 mm.
Rubber bits feel soft, but they need a horse to produce enough saliva to work well. A dry rubber bit can drag on the tongue like an eraser. Rubber bits usually have a stainless steel core inside for strength and safety.
Which bit for which need
For a young horse, or a rider still building an independent hand, a loose-ring, single-jointed bit is a common starting point.
For a horse that falls out through a shoulder, plays with the bit, or has sensitive corners of the mouth, an eggbutt or D-ring bit gives steadier sideways support.
For a horse with a small mouth or a thick tongue, a double-jointed or anatomically shaped bit spreads pressure more evenly across the tongue than a single-jointed bit.
For dressage ridden in a double bridle, use a bradoon with a separate weymouth, fitted as described in "Ring and cheek styles" above.
Bit rules for competition
Bit rules differ between disciplines, and they can change at any time. Before you compete, check the current rules for your discipline, for example the FEI rules or the British Dressage rules, to confirm that your exact bit model is allowed.
