This is from the Charlemagne era. According to A. Demmin (the author of an established book on arms and armour, published 1894), there is a similar example in the Copenhagen Museum. It measures nearly 19cm across.

This form of bit would have been worn by military and civil alike throughout the period of the Crusades. In a modified form, this snaffle bit is still in use today. It is of iron lapweld construction, the central elements being hollow.