Chalk testing a wheel-operated door 

By "lock mechanism" do you mean the mechanism that closes the door and creates a water-tight seal? That mechanism is referred to as a quick-acting dogging mechanism. The quick-acting mechanism on this door does not "lock", so that it prevents you from operating the mechanism and opening the door (similar to a dead-bolt or a thumb-turn lock on standard residential doors). The only way that this door is secured so that it cannot be opened is with a pad-lock inserted through a hasp on the door panel, and an eye on the frame.

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