The TW-23A is a small adapter plate with a round hole. It has a double width exterior porch and an interior cling rod. It is designed to be used with the
TW-5,
TW-5A,
TW-5B, and
TW-5C tunnel for entrance hole interchangeability which is helpful if you are suffering from SREH anxiety or trying to start a colony and prefer to start with round holes. Simply remove the 2 attaching screws and replace the TW-23A with the crescent or WDC adapter plate that came with one of the tunnels listed above. The TW-23A sells for $4.50 each plus S&H.