It's basically an 11 x 4 1/4 piece of card stock that you score in half (5 1/2) and then score again at 2 3/4. The strip piece is also 11 inches long and scored at 5 1/2 and again at 2 3/4 and attached the opposite direction from card base piece. The strip can be any width you like...mine measured at 1 1/2.
It's by a company named Flourishes (remember them??)
They are no longer in business and I've probably had this stamp set for a good 10 years.