See 2, yes they are, the nut is a lock nut to hold it in place when you have threaded the screw to the height you need.1. Fitting of these spikes can dramatically improve sound clarity and frequency response at little expense. They work by mechanically coupling the speakers to the floor, so stabilising any stand or loudspeaker set-up.
2. They should be adjusted so each makes firm contact with the floor and the speaker cannot wobble in any direction.