Micro Nose Stud Size Guide
"Micro" means the top. The gems and balls run about 1.5mm, roughly half the size of a standard nose gem, on the usual 20G, 1/4" (6mm) post. Your piercing doesn't change. Only the visual volume does. Office-proof, strict-parent-proof, and "is she even pierced?" proof.
With a top this small, the post style does the work. L-shapes are the easiest to swap: slide, turn, done. Bones pop in with a tiny ball end. Twisters corkscrew in and hold most securely. All three are here, and the product title says which.
The volume knob goes both ways: