The Fowl Stuff single hole nest box securely fastens to a wooden wall using screws and fender washers supplied with this “complete” heavy-duty unit. No additional bracing or supports are required or recommended. The 6” opening, in the cover, is large enough for most standard chickens, including all bantams and most large fowl hens up to about 6 ˝ pounds. For extra heavy breeds the cover hole may be increased to 8”. Ribbing on the inside of the cover reveals the outline of the area that is specially designed to be cut out for this propose. In some climates vent holes may be beneficial. They can be added as needed using a small diameter hole saw and located on the sides of the box, near the back (wall). Assembled units are 20.25” x 12.5” x 12.5”.