It’s a good idea to print these before you upgrade your printer!
One of the first commonly upgraded parts on the replicator 1 clones are Y-axis bearing blocks, it involves removing one side of the printer and a couple of pulley wheels. Unfortunately this upgrade leaves your printer unusable because the X-axis won’t be square and will need recalibration, if you print you may notice straight lines are angled and circles look oval.
Print these before you upgrade or else have to make something similar by hand, although it’s easy enough to do by hand simply cut a UPVC pipe in half then sand down to match fit the pair exactly measuring with vernier callipers, bear in mind you probably will sand and need to match fit the 3D printed ones too.
To use these: all you need to do is place them on the bars (see photos and illustration) then move the head flush onto these two spacers so that the both sides are touching and tighten up your pulleys.