This is the start of a double sprang. There are 2 middle security cords.
Note: The brown threads are all in front of the upper middle security cord. The red threads are all at the backside of the lower middle security cord.

Then work at both sides of the frame. I did one plait row and one overplait row and then started making holes and keeping them open for 8 rows.

Next the red is worked at the ‘brown side“ pushing it through the holes and closing the holes. Now be careful to move the security cord of the red - not the brown…
Then at the other side work with the brown at the same way…

This is the whole principle. Now you can start playing…

I have made other holes of different length and in the end I have every time used 2 threads in stead of 1 to decrease the width, because I want to use this sprang as feathers for the big bird I want to make for my art project about bullying.