This slide block was design to be use with 8mm rods.

Material that you will need:

2x M2.5 screw + nuts ( 12mm )
2x M3 screw + nuts ( 10mm )
1x M3 screw + nut ( 12mm ) - This one i did use to lock the linear rod.

Original bearing ( ID8mm OD11mm x 30mm )

I did design this parts to be printed without supports.

I do not have an ultimaker so i did not test the parts, if you print this parts pls let me know if they work as is intended.