Single-jointed, double-jointed or straight bit – which mouthpiece suits your horse?
Short answer: a single-jointed bit has one central joint, a double-jointed bit has two joints and a centre piece, and a straight or mullen mouth has no joints. None is always mildest. Shape, thickness, size, cheeks, oral anatomy and the rider’s hands determine the overall action.
| Mouthpiece | Construction | General characteristic | Check particularly |
|---|---|---|---|
| Single-jointed | one central joint | clear folding at the joint | length, curvature and palate clearance |
| Double-jointed | two joints and centre piece | more movement and different tongue contact | centre-piece shape, length and angle |
| Straight/mullen | no joints | continuous, often steadier contact | flexibility, curve and tongue relief |
This is not a mild-to-strong ranking. A thin, unsuitable or incorrectly fitted mouthpiece can cause discomfort regardless of the number of joints.
A systematic way to choose
Check teeth, tongue volume, bars and palate space. Begin with what already works, identify what you want to change, and alter one feature at a time. Over several quiet sessions, observe contact, swallowing, steering, mouth activity and relaxation.
A single-jointed snaffle may suit a horse that likes a simple, defined signal. A double-jointed mouthpiece offers more movement but depends heavily on its centre piece. A mullen mouth may feel steadier to a horse unsettled by moving joints.
Read the detailed guides to single-jointed snaffles, double-jointed snaffles and mullen mouth bits.
Mouthpiece and cheeks
Loose ring, eggbutt, D-ring, full cheek and hanging cheek/Baucher sides alter stability, movement and lateral support. Assess the mouthpiece and cheek design separately.
Competition
Permitted designs depend on discipline, class, age category, material, mouthpiece and cheeks. Always check the current rules before competing.
What your horse’s response can tell you
A change in salivation or mouthing is not automatically good or bad. Look at the complete picture: can the horse take an elastic contact, turn from both reins, swallow normally and remain relaxed through the jaw and neck? An open mouth, head tossing, reluctance to go forward or the tongue coming over the bit can have several causes. Teeth, oral comfort, bridle fit, training and the rider’s hands should be checked alongside the mouthpiece.
Frequently asked questions
Is a thicker bit always milder?
No. Greater diameter spreads contact over a wider surface, but a thick mouthpiece may leave too little room in a small or fleshy mouth.
Should a young horse always start in a jointed snaffle?
Not necessarily. A familiar, correctly fitted and competition-legal design is a sensible starting point, but age alone does not identify the best mouthpiece.
How should I trial a different bit?
Keep the cheek style, size and thickness as similar as possible, change the mouthpiece, and assess it over several uncomplicated sessions. Stop if the horse shows clear discomfort.
Bit sizes in millimetres and inches
Common ByLynga size labels for Ireland are 95 mm (3¾ in), 105 mm (4¼ in), 115 mm (4½ in), 125 mm (5 in), 135 mm (5¼ in) and 145 mm (5¾ in). Measure the mouthpiece itself and check the individual product’s available sizes; inch values are practical rounded equivalents.
Related guides and bits
Compare single-jointed snaffles, double-jointed snaffles, mullen mouth bits and tongue relief bits. Browse all horse bits or explore loose rings, eggbutt bits, D-bits, full cheek bits and Baucher bits.
Competition rules
Permitted bits depend on the discipline, class, age category and the complete design. Before competing, check the current Horse Sport Ireland rulebook, the relevant affiliate’s rules and, for international competition, the FEI Rules & Regulations. Links checked 9 September 2026.