This is a large 3-pice knob from a Naim Olive component (e.g. NAC62, NAC72, NAIT 2, NAP140, HiCap, etc.). This came in a box of spare parts I bought a while ago. These knobs consist of 3 main pieces, the domed cap, the rubber ring, and the back. It is common for the back part to break from over-tightening the grub screw. I created a new back part in CAD that I 3D printed. This back part is much tougher than the original part and uses a standard M3 screw and nut. Note that there are two versions of this olive knob, one designed for a friction fit on a flatted shaft, and one designed to clamp on to a round shaft with a screw. This design should work as a replacement for either version. Condition wise it is good but note that one edge has been smoothed/polished (as opposed to the original matte texture).