The security of a tubular entry set depends on its dead bolt, but not all bolts are of the same caliber. They're graded 1 (the highest), 2, or 3 based on how well they withstand a battery of independent tests, spelled out below.
In one test, the dead bolt is fed into a metal-cutting band-saw blade. Grade 1 and Grade 2 locks can survive this treatment, as well as drilling, punching, pulling, and prying, for 5 minutes.
All graded locks have a finish that remains intact after being assaulted with abrasives, humidity, UV light,
and salt spray.
To simulate how well a lock stands up to wear, a machine repeatedly turns the key, throwing the bolt and then retracting it. Grade 3 locks can go just 100,000 cycles without failure; Grade 1: 250,000.
Each grade is strong enough to thwart a professional lockpicker for 10 minutes.
An assembled door is rammed with increasing force until one component—bolt, strike plate, or screws—fails. Grade 1 locks can take a total of eight such blows, including two of 150 foot-pounds each.