Shires Blue Sweet Iron/Alloy Universal With Roller Link Bit
Sizes :-  4.5" , 5" or 5.5". 
Mouth thickness - 15mm,
Cheek length - 115mm (4.5", 5") 130mm (5.5").

Combines poll pressure and leverage, for a mild gag action. 
The loose brass alloy discs in the centre can help to soothe a fussy tongued horse.
Blue sweet iron oxidizes easily to create a warm and sweet taste, which helps with bit acceptance and encourage salivation.
Please note the blue colour will fade with use.
The addition of brass alloy inserts, produces a warm more palatable bit.