Been tying them on since the early '80s. That looks like some heavy mono on that picture. All you really need is a # test that will support the weight of the fly (jig), as it goes over weed, stick, etc. Anything much heavier will reduce the hook-up during a light bite. Needs to be stiff type of material, as opposed to a soft, supple type. I've been using hard "Mason" leader material. May be better alternatives, but until my spools are empty.....

I tie mostly for fly applications, both fresh and salt, and don't have much experience with this style weed guard on crappie lead head jigs. Not sure if the up turned eye of a jig hook will work well with the mono guard. The mono guard works well with a straight shank hook. Gape space between hook point and the eye of the jig hook is somewhat compromised with the addition of the mono guard.

Try them and if you keep missing strikes, crimp the mono as close as you can to each tie-in point with your hemostats, and it will flatten the mono and weaken it somewhat.