The Cal Royal Products 300 Series Door Closer comes in two versions. One version is the size 3 to 6 spring, which would be for larger exterior doors. The 3 to 6 spring size is for doors 36" to 48" wide. The second version is the size 1 to 4 spring size. The 1 to 4 is considered a Barrier Free door closer, because the spring tension can be turned down to less than 8 pounds of Resistance, making the door easy to open. The 1 to 4 should be used on interior doors and smaller, less than 36" wide exterior doors. This door closer is a standard template closer with a hole spacing of 3/4" x 9-1/16" center to center, which is what we find on many aluminum framed glass storefront doors. This closer has a 5 year warranty and is considered a Grade 1 closer, the heaviest duty rating possible.