Ikea Lack Table Passthrough Couplers

Single caps are helpful if you want to space out the tubes more, while the cluster can be helpful if you want the tubes to be close together. 

If you have spools of filament for an MMU on a spool holder rail below the table, it's helpful to space out the tubes so that they line up on center with the spools. It reduces friction by avoiding sharp turns in the tubing.