The hackamore is bitless, meaning there's nothing in the horse's mouth.
From the therail.blogs.nytimes.com
We put the hackamore on him, and he's been very good.
From the therail.blogs.nytimes.com
I use hackamore bridles so there's no bit.
From the guardian.co.uk
He thought of the hackamore.
From the therail.blogs.nytimes.com
The most significant change Jerkens and his assistant Fernando Abreu made was to change her training bridle to a rarely used bit-less hackamore bridle.