Fender Pentastar
Plastic is correct for 1968 up and metal for 67 back according to information I have found. I actually think they changed in mid 67 so you might find either one on that year. I can't sware this is correct so if someone has more details please chime in.
UPDATE: Here is an eBay auction that is along with my thinking.
http://www.ebay.com/itm/NOS-OEM-Mop...Parts_Accessories&vxp=mtr&hash=item3cc14bd45a