It is important that a coat of arms be easily recognised and so everyday objects were frequently used as clearly identifiable charges – tools Boutell’s Heraldry, J.P. Brooke-Little, Warne, (revised Edition) London 1970, P 69 being a common and important example of these, of which the shacklebolt, a form of padlock, is typical.Fetterlock seems to be another name for the same device