My new ottb gelding has a very narrow, short, tiny mouth. nothing in my (extensive) bit collection suits him, he pulls his tongue back, tilts his head, is totally distracted. None of the behaviours appear in a hackamore. I have already bought a few bits to try since everything I had previously was a 5.5 or 5.25 and he is a 4.75-5. The happiest so far is a thin myler french link d. Others I’ve tried- peewee bit, loose ring with a low wide port, sprenger duo d ring, trust French link full cheek, KK French link loose ring, stubben anatomic French link. Options I am considering next: bomber happy tongue, some kind of leather bit (too thick?) neue schule turtle top ($$$!!!) poponcini super soft option thinking it will shape to his mouth. Also, the Myler he seemed to kind of like is too big, so getting that one a few sizes smaller might be worth a try too. Would love any suggestions, all this trial and error is getting pricey lol. Are the turtle top bits worth it?
My mare doesn’t have a tiny mouth but she does have a low palate and fleshy tongue. And tends to be fussy with her mouth. I have been using a Duo, but yesterday I tried for the first time a Fager Emil bit. It’s titanium and only 14mm thickness. I just hand walked her in it to give her a chance to get used to it, but all signs are looking positive. I was pleasantly surprised by how nice the titanium feels. She definitely played around with it for ten minutes or so but then completely settled. It’s available at Smartpak so you can return if you need to.
My gelding has a small mouth, short, low palate, you can see his tongue squishing out between his teeth. He’s happiest in something with a very low port like a level 2 Myler.
My OTTB went well in a mullen mouth pelham, too. I ride with the curb rein looser, considering that “emergency brakes,” so it’s no more severe than a regular unjointed snaffle.
^^^^i second the Fager Emil. My gelding has a very small mouth space, low palette and a THICK tongue. He’s also very sensitive. He loves the lightness of the titanium, and it’s pretty thin. The joints are also flush vs having loops sticking out like a standard French or oval link.
Pic of the thickness in his mouth. It honestly looks thicker in the Fager promo videos/photos than it actually is in real life, which worked out great for me.
I had a TB mare with a mouth like yours. The only thing she liked was this. ( A genuine Dr Bristol)
She carried it on her tongue which made for great communication. They are REALLY hard to find these days.
Both @Carson_Beach & @ShenanAnna beat me to it, but I vote for a Mullen mouth too.
My Hackney Pony was not happy with the thick rubber snaffle a friend gave me (who had zero pony tack). Yawning, tongue out either side, head up (even for a Hackney 
).
I switched to an uncoated Mullen & he was fine for ground driving < where all communication travels from hand to bit down the lines.
When I got my Mini, one look at his teeny - 3.75" - mouth & low palate & he got a Driving mullen too.
My TB also measures between 4.75-5". The bet and dentist said his mouth is very small, and recommended trying an unjointed bit (mullen mouth). I tried a 14mm one with tongue relief and turns out my horse hates that, but it may be worth a try for you. My horse seems happiest in a myler comfort snaffle.
Myler bits tend to measure a little larger than marked, so keep that in mind on sizing. NS tends to measure a little bit smaller than marked in my experience. If this horse likes the thinness of a Myler, then maybe one of the Mullen mouth styles would work, either a Myler with the swivel and/or tongue relief or something like the Bombers or similar. I had a couple of custom made amulets for a petite TB years ago—standard level 1 Dee with sweet iron and a full cheek slow twist Bristol for when she was feeling a little more spicy.
My OTTB has very tiny mouth…he measures 4.5 inches. I tried a few bits with him. I was using an egg butt snaffle single joint until I tried this bit https://www.smartpakequine.com/pt/shires-blue-alloy-loose-ring-with-mullen-mouth-21121. He rarely plays with his tongue or opens his mouth with this bit.
This bit: https://www.equineessentials.ca/br-sweet-iron-dee-bit-14mm.html
Comes in a narrower width and has worked fantastic for our petite mouth horses. I currently own the full check version, but am buying the D.
I really like the looks of this one. Looks very comfortable.
I have had good luck with a Myler comfort snaffle in a horse with a small mouth/big tongue. He really likes the stability without joints.
I have another horse who goes really well in a turtle top, and for him it is worth the extra expense (though I bought one used, much cheaper than new!). He is a bit chompy, gaping, heavy and leaning in a standard KK or rotated KK mouthpiece and is sensitive to palate & bar pressure (no single joints, thank you). The turtle top is very comfortable to the palate and I notice much less gaping, less leaning, more acceptance of the bit and proper response to milder aids. I’ve tried it on another two horses who also went in a KK type; one horse showed some improvement with the turtle, the other felt mostly the same (but he can go in anything).
This is the one my small ottb hated!
