This is a quote from Myler bits referring to poll pressure with the use of keepers:
| Design: A ring with spindle where the mouthpiece is fixed onto the ring. Spindle top is bent away from ring to prevent rubbing. |
Function: Direct action - when pressure is exerted on the reins same amount of pressure is exerted on the mouth. Sends more of a direct signal than loose ring. Will not pinch or pull through mouth. When spindles are attached to the bridle cheekpiece with the use of a bit keeper the bit offers slight poll pressure. When reins are pulled back the rings tilt slightly forward and offer a subtle downward pressure on the poll.
follow the page down to the section dealing with full cheek snaffles.