The solenoids sit snugly in mounts that slide onto the 20x20 aluminum extrusion pieces. They are assembled using M3 screws and nuts. The sharps and flat notes, at the top of the xylophone, will have a single mount for each note. The natural notes, at the bottom of the xylophone, will use two rail mounts and three solenoid mounts together for proper spacing.
Attach one solenoid mount to the second rail mount using one M3 screw. This will leave an empty space for the third solenoid mount to be attached.
Attach the third solenoid mount with M3 screws so that it's sitting on top of the original solenoid mounts. Assemble 6 total.
Insert the solenoids into the solenoid mounts so that their wires are running up the cable channel on the mount.