PS. As these are rare finds & only referenced in some obscure books/leaflets it will take the right person to ID it, those people are few & far between in the FLO/Museum world. Fingers crossed that it gets a proper ID, if it comes back Norman then they haven't done their homework.
Here are the references:
'W. de C. Prideaux, 1911 'Notes on Medieval Enamelled Armorial Horse Trappings with especial Reference to a Weymouth Find' in Proceedings of the Dorset Field Club 32, 226-38; Anon. 1921 'Harlech Castle: A Recent Find' in Transactions of the Honourable Society of Cymmrodorion, 70; and the discussion in G. Egan ,1991 'Circular-composite armorial mounts' in G. Egan and F. Pritchard, Dress Accessories c.1150-c.1450 ,181-4.'