On a typical exterior door knob, I notice there are 2 parts comprising the barrel latch assembly mechanism – one larger and one much smaller. My question is when a door is closed – are both those pieces supposed to slip behind the strike plate to hold the door closed or should just the larger barrel latch(or whatever it’s called) only slip past the strike with the smaller piece not slipping all the way by the strike? What exactly is that smaller piece for? Thanks very much for a question I have always wondered about.
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The smaller piece does not go into the strike. It's a security piece which prevents the latch from being forced open.
John
Ditto John.
Fool around w it a bit. You'll see when the small one is pushed in, it locks the large one out. It's so you can't "card" the door.
I've met dozens of doors that were not set up correctly. Often times, the weather stripping is out of whack, and in an effort to make the door close tighter, both pieces fall past the strike plate.
Truth be told, in my younger days I think I was guilty of setting a few doors up this (wrong) way.
Harry
That is called a dead latch and it does not go into the strike hole, despite the fact many are installed that way.
The smaller piece in the latch bolt is called the "auxiliary bolt".
The auxiliary bolt stops at the strike plate, the latch bolt goes beyond the strike plate but not the auxiliary bolt.
Test. Open the door, retract the auxiliary bolt and the latch bolt at the same time and you will see that both retract together.
Now, retract only the smaller piece or the auxiliary bolt and hold it there.
Try to retract now the latch bolt and you will see that it won't retract while the auxiliary bolt is fully retracted.
When the auxiliary bolt is in its retracted position the latch bolt can not be retracted, that way you can not unlatch the door with a credit card type device.
Capice?
Right, but it is in fact called a deadlatch. That is the term referring to that type of latch. http://www.kwikset.com/HowToChoose/Replacing/default.aspx . I dont use this brand but about 3/4 down the page in the latch portion it shows the difference between a regular latch and a deadlatch.Edited 12/6/2008 4:51 pm ET by bluejae
Edited 12/6/2008 4:52 pm ET by bluejae