Vktech 4 Pcs Aluminum Open Linear Router Motion Bearing Solide Block (SBR13UU 13mm) Made from aluminum material Model: SBR12UU/SBR13UU/SBR16UU/SBR20UU Shaft diameter: 12mm/13mm/16mm/20mm Cooperate with open linear bearing to ensure excellent sports performance 100% brand new and high quality