What is the best/fastest way to thread elastic through casing?
My mom uses a safety pin.
Here is an example: www.youtube.com/
I use something called Restring-it. You can Google drawstring threader and many brands will come up. Its much faster than a safety pin.
I always used a diaper pin or safety pin....depending on size of casing. You pin through one end of elastic, close the pin, then work the pin through the casing, dragging the elastic behind until you reach the other end of the casing. Take out the pin and sew the ends of elastic and stitch the casing closed
A few years ago, I discovered a nifty tool called a "Purple Thang". It is quite narrow, so it works on many sizes of casings. It has a "slotted eye" that you put your elastic through, then feed it through the casing. It is fairly long, so it works the elastic through the casing a lot faster and easier than a safety pin. And it IS PURPLE. It is my go-to now.
Use a safty pin that is fitting for the opening and attached to your elastic, feeding through one end to the other. This is a simple way and cost effective.