A roller assembly includes a roller having an axial hole and an axle portion disposed in the axial hole to allow the roller to rotate about the axle portion; a sleeve with a first end disposed at a first end of the axle portion and a second end having a fitting portion, the fitting portion being fitted to a carried object, the sleeve has a first blocking portion positioned proximate to a first side of the roller to allow the roller to rotate between the first blocking portion and the fitting portion, wherein one of the axle portion, the axial hole and the first blocking portion has a substance conducive to reduction of friction between the roller and the sleeve.