Whelp, to be honest, this lock isnt with me yet. It should be here tomorrow or Monday. The seller said that the guard keys turned the cylinder but didnt open the lock. And the fact that it says guard, makes me think this is a prison lock or a bank lock. Local mastersmith was perplexed by the guard cylinder. So I went with the old adage, "If you've never seen it before, buy it." Im confident this is a Dual Custody Padlock. I plan on Picking the change cylinder just to confirm.