Bring it to your hardware/home improvement store and find the hex nut that fits in the slot, then match it with whatever bolt type you prefer.. my DM10X has hex key (Allen) but if you can get the size to match a lug and prefer to use a drum key then go nuts (pun intended?). Just make sure the nut fits snuggly so it doesn't spin as you tighten and cut into the slot and ruin the gripping.