This was designed as I had a problem in folding my drone for packing or transporting. The legs get loose and had a slight play. So I took the original design of Bernhard Claussen (You may find it here https://www.thingiverse.com/thing:889039) and redesign it to hold two 16mm rods together. This can hold the legs to the center arm (for 650 owners; I'll add another design).