This monogram is from a 14th century Manuscript Alphabet book which resides in The British Museum in London, England. 

Monogram: Y

Accents/Accessories: Smooth background; Jump ring bail; Raised central monogram; Oxidization

Size: 45.72 x 25.40 (1.80 x 1 inches)

Weight: 9.70 grams (0.34 ounces)

Sterling Silver Chain as shown: 16 inches - $25.00 or 18 inches - $35.00