This is a Collins run out bit, according to Dr Mal's encyclopaedia of bits the design was patented on September 26, 1950 by George H. Collins of Lynbrook, NY.
It is a lightweight aluminium bit.
It has a straight mouthpiece and a round disc with slots for cheekpieces on each side.
A central bar passes through the mouthpiece, it is curved at one end. There is a ring for the reins on each end of this bar.
When the curved side is pulled it compresses a spring in the opposite cheek - this causes pegs or spikes to protrude and press into the horse. The theory is that this discourages running out to that side - it is rather like some ancient chariot bits.
One cheek plate is stamped "Pat.Reg D 160 249
Dimensions of bit : Mouthpiece 11.5cm (4½"), Cheek plates 8cm (3¼") Weight : 400g (14 oz)
