This is a 1x2x3 "plus" cube puzzle design.
it has a simple pin mechanism to snap everything together. No additional hardware is needed.
Make sure the end pieces move freely in the grooves before assembly. The fit should be tight, but you should be able to turn them.
Assembly is easy,... place the pin into one of the center pieces. Place the four end pieces into each of the slots around that piece. Now take the remaining end pieces and place them above the first four. Finally, get the other center piece started, make sure everything is aligned, and snap it all into place.