specifically you'd want this
http://www3.towerhobbies.com/cgi-bin...?&I=LXHMF3&P=C
or
the same size CB nut here (scroll way down)
https://mecoa.biz/shopdisplayproducts.asp?id=82
I use the CB nut on my dle 20,, works great,,, you do want to double nut if possible,,, good luck