fast eddy
i bought four of those bearings from same seller
used them on my gantry , ended up bin ing them , before you buy them ask the seller for a data sheet because i dont think they are double row bearings.
there is sideways freeplay in them no matter how much you preload them.
i tried to find them online using the number on the bearing to no avail

the only others i could find are these ones at euro bearings £20 each

http://www.linearonline.co.uk/acatalog/Bearings.html#

i gave up and bought 16mm full supported rail , far superior