A one-piece siege weight breastplate, formed with a medial ridge and a centrally notched flange at its lower edge (small tear), each side of the chest fitted with a stud for the attachment of a shoulder strap. Shot proofing to the left, the brestplate is circled with holes for attaching a liner. 

The partial outward turns at the neck and armpits are what suggest to me that this piece may be English, Circa 1650. The English Armourer Richard Holden was applying this technique to heavy shot-proof breastplates at this time.

Dimensions:

Height: 16 Inches (36.83 cm)

Width: 14 Inches (35.56 cm)