They are made from 1/4" shock cord and 2 plastic snaps. You can find the cord in 20 ft lengths in the Kayak section of many sporting goods stores, and sometimes you can find the snaps there. I usually go to a kayak shop to get them and they have a variety of ends that can be used for many things with the shock cord. The last ones that I bought I found on line. You can do a google search to find the snaps. See pictures below- one is the package that the snaps were in which I bought on line for less than $.50 each. To get the fittings on the cord, you take a 1 inch long piece of electrical tape, split it in half, wrap one of these pieces around the end of the cord to keep the outer cover from unraveling, slip the collar over the cord, than insert into the snap, , slide the collar forward over the end of the snap with pliers or channel locks and one end is made up. I then wrap the cord around the cover to estimate its length and try to make it where there is slight tension when the 2 snaps are connected around the cover by itself. When you have estimated the length you need, wrap a short piece of full width electrical tape around the shock cord where you want to cut it. Then cut in the middle of the the tape with a razor blade, then make the second snap up to this second end of your cord. Connect the 2 hooks and then slide the cord over your unit and cover. I slide the cords where they are riding just below the knobs of the units, and I have never lost a cover with one of these and they last forever as long as they are not exposed continuously to the sun.