Ever print some mechanical parts and only later realized that it requires LM10LUU bearing and not LM8LUU ones you had prepared? This might be useful for you.

An adaptor to fit LM8LUU bearing (dia. 15mm) to fit on LM10LUU (dia. 19mm) slot.

Note that it's not a 'real' adaptor since the length was kept the same as LM8LUU (45mm) instead follows LM10LUU (55mm), so may have some limited use.

Depending on your 3D printer tolerance, this prints fairly precise fit on my Hypercube printer with 0.4mm nozzle @ 0.3mm layer height. But if it doesn't fit nicely or you want to edit further for say LM8UU (shorter variant), you could edit the provided Solidworks or configure slicer setting for tolerance.