This is an 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.
The mouthpiece of the bit is stamped "Whippy & Co" and "TM".
The firm of Whippy Stegall & Co. was a prestigious saddlery company established in the 1790's, they operated at North Audley Street until the second World War.
The bit still has its original curb hooks and rein rings.
It has a leather curb strap which is probably a modern replacement.

Dimensions : Mouthpiece 4¾ (12cm), total cheek length ( not including curb rein rings) 7" (18.2cm)
Weight : 441g (15½oz)