Kennedy half dollar coins dated 1965-1969 contain only 40% silver and are known as 40% clad half dollars. In 1965 the Mint's removing silver from dimes and quarters, and reducing the silver content of half dollar coins to 40%, heightened the hoarding of all 90% silver coins but especially the 1964 Kennedy half dollars. US half dollars 1964 and earlier contain 90% silver. 1966 is a nice find. Well done on the clean-up.