The size you need is close at hand with this set of two- and four-fluted end mills. Includes

sizes 1/4”(3/8" shank) ; 3/8"( 3/8" shank) 1/2” (1/2” shank); 5/8” (5/8” Shank) and 3/4" (3/4" shank),

all in a wooden case.