ANSI grade is a durability and strength rating for locks and door hardware, set by the ANSI/BHMA A156 series of standards. Grade 1 is the highest, built for the most cycles and the heaviest use; Grade 2 is a solid residential upgrade; Grade 3 is builder-grade and the minimum accepted for a home.
Two deadbolts can look the same on a shelf, carry the same finish and cost very different amounts, because the thing that separates them is not visible from outside. ANSI grade is how that difference is written down.
It is a rating, not a marketing word. Hardware graded to a standard has been tested to it, which is why "heavy duty" stamped on a box tells you nothing and "Grade 1" tells you quite a lot.
What the grade is measuring
The ANSI/BHMA A156 standards cover locks and door hardware, with separate documents for bored locks, mortise locks, cylinders and auxiliary locks. Each sets the tests a product must pass, and each defines what it takes to reach a given grade within that document.
The tests fall into three families. Operational testing cycles the lock repeatedly and measures whether it still works. Strength testing applies force to the parts that have to resist it. Security testing measures what happens when somebody attacks the hardware rather than using it.
- Cycle life: how many operating cycles the lock survives before it stops working reliably.
- Strength: how much force the bolt, the cylinder and the case withstand.
- Security: resistance to the attacks the standard defines for that product type.
Grades 1, 2 and 3 in practice
Three grades are in common use, and the difference between them is the difference between hardware that fails in its third year and hardware that outlasts the door it is fitted to.
- Grade 3 is builder-grade. It meets the minimum for residential use and is what a house is typically fitted with when it is built.
- Grade 2 is a solid residential upgrade: more cycles, more strength than the minimum.
- Grade 1 is commercial-grade, rated for far more cycles and higher forced-entry loads than either of the others.
Why the grade alone does not secure a door
A Grade 1 deadbolt screwed into a softwood jamb with a short strike is still a door that can be opened with a foot. The grade describes the hardware; it says nothing about what the hardware is fixed to.
Three things matter as much as the grade: the length of the bolts holding the strike into the frame, whether the bolt throw is deep enough to sit properly in that strike, and whether the door and frame are still square enough for the bolt to line up every time. Hardware that does not line up is not being used at its rated strength, whatever the box says.
How to ask for it
Ask for the grade by number, and ask which A156 standard it is graded under. A supplier who cannot answer is not selling graded hardware, and one who answers "heavy duty" has answered a different question.
If the grade is not printed on the packaging or in the manufacturer documentation, treat the product as ungraded until proven otherwise. It is a test result, so it comes from somewhere.
Related:Wikipedia: dead bolt