A full mortise hinge consists of two leafs, one with two knucles, the other with two.
The five knuckles make up the barrel which accepts the hinge pin on which the door pivots. I have seen doors with the three knucles on the door and some with two.
There are all kinds of sites on the www with information on hinges, nomenclature, how many hinges needed for a given size door, etc. But nothing to answer the following quetion.
Is there a preferred leaf to be installed on the door and why?
I’d install the leaf with three knuckles on the frame and the one with two knuckles on the door. This is because both of the knuckles on the door will then be resting on the knuckles of the leaf on the frame, instead of just two of the three. In addition, it’s a bit easier to remove the door from the hinge if you use the three-knuckle leaf on the wall.
If it’s a loose-pin jinge you don’t have a choice. It depends on which side of the door the hinge is installed. On one side you have 2 knuckles and if it goes on the other side you’ll have 3. The head of the pin always has to go up.
[trim carpenter belt on]
The three knuckle portion always goes on the jamb. I wish I could tell you why but it was never explained to me, just “do it this way or you will get laughed off any jobsite you ever step onto.”
UPDATE: I just checked all the doors in my condo, my gf’s condo, and the basement, entry, and locker room doors; all with the 3 knuckle portion on the jamb.
I’m glad I don’t do the actual work anymore, that belt is hell on my back. Telling the crews what to do is much easier.
As chaparralv8 says.
Another way of looking at is to count the bearing surfaces. You get two, no matter which way you mount the hinge. If you mount the 3 knuckled piece on the door, you may as well cut off the bottom knuckle for all the support it supplys.
With 3 knuckles on the frame, the top knuckle fixes the pin, and the other two support the weight of the door. You could get away with 2 and 2 knuckles, but I’ll bet such hinges would wear out much faster.
I haven’t seen a worn-out door hinge on a house door. Perhaps if we were talking about Wal-Mart hinges this might become a factor.
Maybe a little clarification…
If the 3 knuckled bit is on the frame, then the top and bottom knuckles are fixed, and hold the pin in a fixed vertical position. If the 3 knuckled piece is on the door, then the pin is only held vertical by the two closely spaced knuckles on the frame. That arrangement is less able to handle torque, or slop (via wear or poor manufacture) in the knuckle holes.
With the exception of one, all the doors in my apartment have the three knuckled bit on the door. This includes the recently installed pre-hung unit.
I just looked at the dorrs in my house. It looks like they are split about evenly with half have 3 knuckled hing on jam and the other half with 3 knockled hing on door.
Let me guess. As you face the door to pull it open toward you half the hinges are on the right and half on the left. Right?
To the best I could tell, from several online sources of hinges, most is not all door hinges are identical in the way the knuckles are arranged with respect to the leaves. Thus a door opening toward you with the knob on the right (a right hand door) will have the hinges on the left with three knuckles on the jamb and two on the door.
A left hand door, opening toward you will have three knuckles on the door, two on the jamb.
BTW the knob on the pin and bottom of third knucle is the “Finial.”
3 knuckles on jamb to support the weight of the door better as well as holding the door on the jamb better security wise. Very little difference on the security part
I think that’s the consensus everyone arrived at 18 years ago, too.