The other pieces are the frames which exactly match the inserts. The pieces in order from the outside in are (1) Outside Frame, (2) Large insert twist die, (3) Inside Frame #1 (4) Medium twist insert die, (5) Medium twist inside frame, (6) Small twist insert die, (7) Small rectangular die.
Becca always does that with her what I term frame dies. The idea is if you want to put in a pattern on another shaped piece of cardstock, then you use only the insert die. If you want to create a matting back for a card in the exact shape of or the insert you use the outside frame and the insert. If you want to create a photo frame, you use the outside frame, the insert and the inner frame.
It is the same for Candlewick, hemstitch dies, it's just that with the twists they fit snugly in one another so that you cannot see it from the rendered drawing.
I was trying to upload an image. I will see if I can post it somewhere else. I have posted the image of the die in My Gallery. Look for Elegant Twists as a keyword.