This part fits into the Q-Snap tube to make a longer frame side. This single piece is if you need to replace one of your extensions because your dog chewed it up or something. I personally use these on the 17 x 17s to make them as big as I need to while beading projects.
*Please note: they need to go at parcel rate as they do not fit through the gauge at letter rates for postage. They are very light though and will not make your parcel heavy.