This is a heavy antique steel curb bit.
It has a straight mouthpiece which can rotate.
The ends of the mouthpiece pass through slots in the long straight cheeks. This allows the mouthpiece to move up and down slightly and the cheeks can rotate independently.
One cheek of the bit is stamped "Cockshoot" and the other "Manchester".
Joseph Cockshoot started a coachbuilding company in 1744, it became Cockshoot Ltd in 1895, this bit probably dates to the late 19th century.
The bit still has its original curb hooks and rein rings.
There is some light surface oxidation on the bit which could be burnished off.

Dimensions : Mouthpiece 5¼ (1cm), total cheek length ( not including curb rein rings) 8½" (21.8cm)
Weight : 753g (1lb 10oz)