If you have older K&M boom stands that are starting to sag even when you tighten the boom up hard, this will fix it. They do wear out in time so it's good to keep some spares around to maintain your stands. I also modified a stand and that made the boom mounting loose so an extra one of these filled the gap.
For such a basic, cheap part, it's crazy not to have them since they are so important to making your stands work properly. Now I know I can get them easily and cheaply from Thomann with my other orders I'll maintain a supply