The slot is 1.75 inches long and about 2mm wide. This prevents binding when you fold the
flap over to adjust the amount that the bouncer is cupped toward the front. Although I used
thesew-on type velcro,I put a small piece of double stick tape under it to hold it in place
while sewing. My problem with the adhesive type velcro is that heat melts the adhesive, so
when you use it outside on warm days, it tends to fall off after a couple outings.