The Myler HBT Shank with Sweet Iron Low Ported Barrel Narrow (MB 43LP, Level 2-3) offers significant relief for your horse's tongue as the narrow mouthpiece does not rotate on the tongue and there is a generous 1 1/4" port.
Details
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The Basics: Sweet iron with copper inlay. Sweet iron will oxidize naturally over time, is harmless to horses, and its sweet taste encourages salivation.
Level Up: Myler's unique "level" system means there's a bit for your horse no matter their training. Level 2-3 bits offer precise control through ported mouthpieces that relieve your horse's tongue, however there will still be some degree of pressure for correction. Ideal for moderately experienced horses or horses who show resistance to Level 1 and Level 2 bits. 
\nBenefits of an HBT Shank: HBT Shanks are curb bits with shorter purchases than flat shanks. They use a bit of leverage and ideal for trail riding as the short shank design makes for easy grazing.
\nIndependent Side Movement: Entire shank moves independently from the mouthpiece which means more control and clearer communication between you and your horse.