This Park tool comes in handy if you have muiltiple size bolts. This comes with a 4mm, 5mm and a 6mm. These are the most common sizes when working on a scooter. the 4mm comes in handy when your working on your brake, 5mm is what you will need when working on clamps, standard axles and compression bolts. The 6mm is what you will need when working on grade 8 axles and Tilt style hardware.