I don't know much about these things, but it seems that the the two halves of the mold fit together via the four posts (on one half) and the four holes (on the other half). The plastic or whatever must be injected through the hole in the center of the mold, and then makes its way to the four chip molds.

Incidentally, here are some molds from my web site:
http://www.antiquegamblingchips.com/steel_mold.htm
(I think I'll take the pictures from the auction and add them to my web site.)

Robert