You always amaze me with your knowledge of Spanish coinage. I'll have to weigh it when I get back home but my guess is that it is a 1/2 Real based on how thin it is. Any idea on the range of years these were minted? I'm sure this one circulated quite a while before being dropped.
The mint years for the 1/2R were 1668-1697 inclusively though several years were omitted. Assayer's initial 'G' through 1674; 'L' thereafter.
The mint years for the 1R were only 1668 and 1692; the 1668 had one of two assayer initials; either a "G" or a "L"; the '92 had "L".
Don....