15PCS Size: 8mm, 10mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm. Stamped markings make all model numbers easy to keep, read and quick. The recessed hexagonal nut is easier to embed, which can grasp the stubborn fasteners without falling off.