Genuine Myler loose ring snaffle with sweet iron comfort barrel mouthpiece. This is the MB02.
In good condition, sweet iron has oxidisated with is completely normal.
This bit is a "size 6" as Myler only produce 1/2" increments, however it actually measures closer to 6.25" - shown in the pictures.
This bit with the sweet iron mouthpiece has now discontinued so quite rare to find second hand.