Ancient wisdom suggests putting two nuts back to back on the prop shaft to avoid the prop from getting loose. In my limited RC experience, I haven't seen an engine that already comes with two nuts, so I usually add a lock nut to be safe. My new ASP .91 FS, however, already comes with two nuts. The second nut has a part that protrudes out and gets lodged in the first nut (see picture.) My questions are:

- What is the purpose of the piece that protrudes out on the second nut?
- I take it with this arrangement I am OK and don't need to add/change anything else for added safety?

Thanks.