This picture shows how little cuts were made and fold over to then sew them with a sewing machine.
When it was difficult to hold the cut flaps when being sewed, the idea came to first glue the pieces on the inside so that it is easier to sew.
Because it stayed in place, it was directly sewed upon the elastic part.
This came with the problem that there was a gab, because it was sewed to far from the edge. Of course if it was sewed this way it would always have a little gab where filth can accumulate.
The problem with 48b was solved when an extra stitching was applied
After seeing the fun aspect of sewing with zigzag pattern. It was used to attach the top of the casing.
The other side of the prototype is completely made of the technique used in 48d