I have a new (old) bicycle, and I am in the process of disassembling it.
I arrived to the bottom bracket (with a cottered crank), and unscrewed the ring without problems, but then I'm faced with a part that I don't think I've seen before (circled in yellow in the picture below, the part next to the frame with the threads and a strange "groove").
I've disassembled several BB, but this is new to me (normally I have a nut and unscrew it, I bet this may be another kind of nut), and I don't know if this can be removed and how?
Is this something that I can unscrew, and does anyone know of the technique/tools to do it?
(By the way, the other side has the same part, but as far as I can see there is no thread (visible at least))