Cu-Ni 38.6mm diameter, 28.6gm.  By Pobjoy Mint. 

ISLE OF MAN  ELIZABETH II 1979  Her diademed, draped bust right. Mintmark PM below.  R. TERCENTENARY OF MANX COINAGE · ONE CROWN · Nine Manx coins arranged in a circle. KM45a. Almost FDC.  In case of issue, with certificate. 

Depictions of coins are unretouched images of the actual item offered for sale.