The TW-1A inner/double width exterior porch is an interior porch with an exterior porch that is twice as wide as the TW-1 porch. The double width exterior porch was designed to help the Purple Martins enter and exit SREH without having to struggle so much. The double width exterior porch is for use on gourds which have the SREH cut directly into them. It can be used on natural gourds or Supergourds. It is mounted by cutting a slot 3/16" to 1/4" below the bottom of the SREH. The TW-1A interior/double width exterior porch is a little more difficult to install than the TW-1 porch. After slipping the porch into the slot you have cut, you will need to have some pvc clear cleaner and pvc glue. The support tab, which is provided, must be glued underneath the porch from inside the gourd. Then, a small amout of caulk added around the slot on the outside of the gourd to prevent toenails from being caught and to hide the slot from view. The porch is made of 2mm thick Sintra and has grooves cut into it so the birds can get traction. The TW-1A sells for $3.50 each plus S&H.