Features: Thickened Steel: All use international standard thickened steel, never deformation. 12inch-20inch children bicycle training wheel: Two back wheels form the triangle stable structure, no need parents no falling down more stable and secure. Noiseless rubber wheel: Noiseless rubber wheel, more abrasion-proof, more noiseless safer. artistic and beautiful. All use international standard thickened steel. never deformation which is thicker. Auto-locking Nut: We use the autolocking nuts to insure kids safety. Safer than ordinary nuts, won't be loose after screwing on. Specification: Size: 24.4 x 19.9 x 2.5cm Application: 12-20inch Material: Northeast maple plank, steel, PU Color: Blue Package List: 2 x Wheels (with fittings)