Summary

I am using these spacers very frequently in my builds. Seems like cheap stuff, but they are essential and without alternative. opinion alert ;-)

1.5, 4 and 6mm versions are needed to align axle clamps (centerhole 30mm high) and M8 bearing blocks and hex bearings blocks (centerhole 36mm high).

10, 15 and 20mm are just for extending a profile to overcome a specific distance.

20mm is the shortest offset that can be achieved with Infento std. parts (either 2 swivel plates face to face, or profile connectors type A, or the old T-joint).

The square holes are designed to work with T-positioning blocks.

The noses may not hold a huge shear strength (though I didn't break a single so far), but they don't really need to, as long as you set these spacer well under compression with the M8 center bolt.

0.4mm nozzle diameter is recommended.