VEVOR 2PCS Linear Rail 0.78-42 Inch, Linear Bearings and Rails with 4PCS HSR15 Bearing Block, Linear Motion Slide Rails plus for DIY CNC Routers Lathes Mills, Linear Slide Kit fit X Y Z Axis
Are the ball berings in HSR15 have double ball berings on each side of the rail meaning touch the rail on the bottom side and independently on the top side of the rail or there are only bering on the bottom on each side?