Very well constructed and relatively easy to assemble.  I put them into header boards above the opening and it feels very secure.  There is a large gap between the doors as others have reviewed.  Tolerance are pretty tight on the “U” shaped bracket that holds the outer rail.  I used a socket wrench and had a little bit of an interference with the upper nut install. A standard metric unit flat wrench would help with the tight installation tolerances, but will take longer to install - there is no room for using a powered equipment.