I began with this template. My cardstock measured 8 1/2" x 5 1/2".
My first score line was at 4 1/4".
After that I cut along the red indicated lines. PLEASE MAKE SURE YOU STOP YOUR CUT ALONG THE SIDE AT THE 2 1/8" POINT. This is measured from the centre fold (4 1/4" score line).
You can see the score lines and cut lines on my base cardstock of Heavy Whisper White.
This is the Heavy Whisper White with the sides folded along the score lines. Basically you will fold a "mountain", a "valley", and then another "mountain". You can see already how the centre cut area is free to swing as you open the card to stand it as an easel.
This is the inside of the card. You can see how the easel works from underneath. I've made this into a birthday card, leaving one "word bubble" empty so that a personal greeting can be written inside.
This is the same card from the front. I love the 3-D effect, don't you?
And this is the card closed for mailing. A perfect 4 1/4" x 5 1/2" card.
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This is the template for the 5 1/2" x 5 1/2" card.
After that it was just a matter of following the cut lines and score lines exactly as shown for the 4 1/4" x 5 1/2" card.
Good luck with your Swing Easel card(s). If you have any questions or problems, just let me know.