Nathe 20mm Mullen RNF Bit
$469.90
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Horse Bits · Thermoplastic Mouthpieces
Nathe Bits
Nathe gives a horse with a sensitive or fussy mouth a thermoplastic mouthpiece that stays temperature neutral and sits steady on the tongue, so he can settle into the contact instead of arguing with the bit.
By the Tack of the Day Product Team · Updated November 2026
Shop by Bit Style
Find Your Fit
In the Spotlight
Nathe is best known for the mullen mouth and the loose ring snaffle, and these two shelves put the two side by side.
Nathe mullen mouth bits
Nathe mullen mouth bits in flexible, ported and full cheek styles.
Nathe loose ring bits
Nathe loose ring bits in single and double joint mouths, 55mm and 70mm rings.
The Nathe Edit
Nathe bits built on a thermoplastic mouthpiece, from mullen to Weymouth
The numbered sections cover the thermoplastic mouthpiece, the mullen and jointed mouth shapes, the cheek pieces, and the pelhams and Weymouths, then explain sizing and how to match a Nathe bit to your horse.
The material
Nathe thermoplastic mouthpieces for horses that hate metal
Nathe thermoplastic mouthpieces suit horses that fuss with metal because the mouth is plastic, and the vendor describes the material as anti-allergic, food safe and solvent free. The exterior stays temperature neutral, and on most styles a steel core stays flexible in the cold. Nathe is a go-to option for horses with sensitive mouths, which is why the mouthpiece comes first on this page. The Standard 20mm Thermoplastic 55mm Snaffle Bit and its 70mm version are the plainest examples, a 20mm thermoplastic snaffle with a stainless steel joint. The 15mm Double Joint Hard Thermoplastic 55mm Loose Ring Bradoon uses stainless steel joints rotated 45 degrees for more comfort. The 20mm Mullen Mouth Bit w/Set Small Rings and the Pony Standard Snaffle Bit 16mm have no steel core. Look elsewhere if your horse goes best on copper or sweet iron, because Nathe cheek pieces are stainless steel.
Shop thermoplastic bits, plastic bits, the Standard 20mm Thermoplastic 70mm Snaffle Bit or the 15mm Double Joint Hard Thermoplastic 55mm Loose Ring Bradoon.
Mouth shape
Nathe mullen mouth and jointed bits for a quieter contact
Nathe mullen mouth and jointed bits give a quieter contact because each mouth shape is built to spread or soften pressure on the tongue. The flexible mullen lists steady, even pressure on the tongue. The ported mullen relieves the middle of the tongue and suits horses that pull the tongue up, in soft, standard and hard versions of the 15mm and 20mm Mullen Mouth Loose Ring Bit. The Mullen Mouth Loose Ring Snaffle Bit 20mm Flexible w/Copper Link adds a copper link the vendor says fosters acceptance and stimulates saliva. Jointed styles include the 18mm Sensogan Middle Double Joint, angled 45 degrees to lie flatter, and the 18mm Double Joint Control, which locks like a straight bar under pressure and unlocks when the contact softens. Look elsewhere if you want a fixed, non-flexing mouthpiece.
Shop mullen mouth bits, single joint bits, multiple joint bits or the Mullen Mouth Loose Ring Snaffle Bit 20mm Flexible w/Copper Link.
Nathe single-jointed bits
Nathe single-jointed bits in 18mm and 20mm, loose ring, D-ring, eggbutt and three-ring.
Cheek action
Nathe loose ring, three-ring and full cheek bits by action
Nathe loose ring, three-ring and full cheek bits differ by action, so the cheek decides how the bit speaks to the rein. Loose rings in 55mm and 70mm move with the horse's mouth. The Eggbutt Bit 18mm lies steady and does not slip through, and the 18mm Single Joint D-Ring pairs 70mm rings with cheek guards. The Full Cheek Snaffle Bit 18mm Single Jointed gives lateral contact that Nathe lists for horses that fall out toward an obstacle, a style handy hunters use for tight turns. The 20mm Double Joint 3 Ring has three rings for adjusting leverage. Look elsewhere if you want a gag for a newer rider, since Nathe lists its gag bits for experienced riders only.
Shop loose ring bits, multi-ring bits, eggbutt bits, D-ring bits or full cheek bits.
Nathe multi-ring bits
Nathe multi-ring bits with 18mm and 20mm mouths and adjustable leverage.
Double rein
Nathe pelhams and Weymouths for double-rein control
Nathe pelhams and Weymouths give double-rein control through a thermoplastic mouthpiece rather than a steel bar. The 15mm Hard Port Long Cheek Pelham gives even impact on the mouth, neck and lower jaw, and Nathe lists it for horses that resist the reins. The Soft Mullen Mouth Long Cheek Pelham 15mm has a low port and is listed for strong horses, with rein options that adjust poll leverage. The Short Cheek Weymouth Bit 15mm is ported and gives quick effect with less poll pressure, and the 7cm Long Cheek Weymouth gives a slightly delayed signal with more poll pressure. A Weymouth goes in a double bridle with a bradoon, such as the Bradoon Bit 15mm Single Jointed. Look elsewhere if you ride on one rein with no curb action, because the loose ring and eggbutt snaffles above fit that better.
Shop pelham bits, Weymouth bits, Liverpool bits or the Bradoon Bit 15mm Single Jointed.
Nathe pelham bits
Nathe pelham bits in 15mm and 20mm, with soft, hard and flexible mouths.
Sizing
How to size Nathe bits: 15, 18 and 20mm thickness plus width
Nathe bits are sized on two measurements, width and thickness, so check both before you pick one. Width is the mouthpiece length between the rings, listed from 110mm to 145mm in 5mm steps, plus One Size on a few styles. The simplest way to find yours is to measure the width of a bit your horse already wears, ring to ring. Thickness is the number in the style name, 15, 16, 18 or 20mm, and each Nathe line sits in a set range, as the table below shows. A thinner mouthpiece leaves more room in a small mouth, and a thicker one fills it more. If your horse falls between two widths, open the filters below and compare the styles at each before you order.
Shop Nathe bits or filter by width: 125mm, 135mm or 145mm.
Which bit
Which Nathe bit suits your horse: sensitive, strong or fussy
Which Nathe bit suits your horse comes down to what he is telling you through the contact. For a sensitive horse, the 20mm Mullen Mouth Bit w/Set Small Rings limits sliding, does not pivot to the outside, and has a ported mouthpiece to relieve tongue pressure, with built-in guards for the lips. For a fussy horse that will not chew or accept the bit, the Mullen Mouth Loose Ring Snaffle Bit 20mm Flexible w/Copper Link lists improved chewing activity and saliva flow. For a horse that pulls or leans, Nathe lists the Gag Bit 20mm with Flexible Mullen Mouth, with gag action and bit guards. Look elsewhere if you are not yet confident in your hands, because Nathe lists that gag for experienced riders only.
Shop mullen mouth bits, the 20mm Mullen Mouth Bit w/Set Small Rings or the 20mm Mullen Mouth Full Cheek Gag.
Questions riders ask
Nathe bits FAQ
What is a Nathe bit made of?
Nathe bit mouthpieces are thermoplastic, which the vendor describes as anti-allergic, food safe and solvent free, and most have a steel core. Cheek pieces are stainless steel. Two styles, the Pony Standard Snaffle Bit 16mm and the 20mm Mullen Mouth Bit w/Set Small Rings, have no steel core. Shop Nathe thermoplastic bits to compare mouthpieces.
Is a Nathe mullen mouth bit good for a horse that leans or pulls?
Nathe lists its Gag Bit 20mm with Flexible Mullen Mouth for horses that pull or lean on the bit, and the soft and hard ported 15mm Mullen Mouth Loose Ring Bits as suitable for strong horses. The gag is for experienced riders only. Shop Nathe mullen mouth bits and pick the cheek action that fits your ride.
What is the difference between Nathe 15mm, 18mm and 20mm bits?
The number is mouthpiece thickness. 15mm covers the ported mullen loose rings, bradoon, Weymouth and pelham mouths. 18mm covers the jointed snaffles with eggbutt, D-ring, full cheek and three-ring cheeks. 20mm covers the flexible mullen, gag, Liverpool and set-ring styles. Choose the style first, then check the thickness in the sizing table above.
How do I size a Nathe bit?
Measure the width of a bit your horse already wears, from ring to ring along the mouthpiece. Nathe lists widths from 110mm to 145mm in 5mm steps, plus One Size on a few styles. Check the thickness in the style name too. Filter Nathe bits by your width to see the styles that match.
Which Nathe bit works with a double bridle?
A double bridle takes a Weymouth and a bradoon together. Nathe makes the Short Cheek Weymouth Bit 15mm and Long Cheek Weymouth Bit 15mm, and the Bradoon Bit 15mm Single Jointed or the 15mm Double Joint Hard Thermoplastic Bradoon to pair with them. The curb chain is not included. Shop Nathe Weymouth bits and add a bradoon.