I had two of those cheap thread cone holders from JoAnn Fabrics. I had them loaded with my thread and hanging on the wall near my longarm. Last week they fell off the wall -- one of the crossbars had come loose and brought both down. I shouldn't have loaded them with the cones, but I had no alternative. So, I charged my husband with fixing them and making them more sturdy. (Keep in mind that my husband is an engineer -- retired, but once an engineer, always an engineer!) This is what he came up with as an alternative: I can tell you it's sturdy and actually screwed into the wall.
We (I had to hold while he used the battery powered screwdriver), hung it this morning. He was surprised to find that I filled them all. So, he was redesigning as we went -- "should have put another rack by raising the top one and fitting another between the two." (There are 10 pegs on the top holding those cones). I will not be surprised if he makes me another over the next few weeks with three racks! Either way -- I love it. I have more thread that I have on a shelf and in a drawer, but these are the ones I use the most -- all Signature cotton.
Being married to an engineer!