The balls can be made in many different, but similar ways. The center of most balls is cork, rubber, or a mixture of the two. It is sometimes layered. Yarn and twine and sometimes wool are wrapped around the center core. A leather cover is put on, in two pieces, and stitched together using 108 stitches of waxed red cotton thread. Official Major League balls sold by Rawlings are made to the exact MLB specifications (5 ounces, 108 stitches).