Product description:
Make sure you measure the actual outer diameter of your bike frame seat tube
28.6mm clamp suitable for frame seat tubes 27.8mm – 28.8mm, 31.8mm clamp suitable for frame seat tubes 30.2mm – 32mm. 35.9mm clamp fits frame seat tubes from 33.5mm to 35.2mm.
Please refer to the third or fourth picture to choose the desired size.