The Colin Miles Petros Williams is built with a Williams cheekpiece, which allows for multiple rein positions. If attached to the main ring the bit acts as a loose ring, but when connected to the bottom ring it promotes pole flexion by creating more positive poll pressure. The Williams cheekpiece also helps to prevent drifting.
The Petros mouthpieces rotate stopping the horse taking hold of the bit, with the additionj of central copper discs giving the horse somehting to play with.
This bit is lightly used and in good condition. The sweet iron has some oxidisation which is completely normal.
These bits retail at around £110