I need to install a door knob and latch on this old interior door (the cuts in the door were there when I bought the house, and the original hardware is long gone):

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Could someone please tell me what kind of lock set I need, and whether I should be able to buy it off-the-shelf? I can't find any in my box store that fit.

I think it might be called a mortise lock, but the only locks of that type that I can find are too big for the opening on the side of the door.

  • 3
    AFIK that is indeed a mortise lock. Take your picture and make measurements and go to a serious locksmith store. They I'm sure they can tell you what kind of lock will fit in that mortise. Jun 29, 2019 at 1:51

1 Answer 1


need to install a door knob and latch on this old interior door

If you really need to do it, stop screwing about and drill the door for a standard modern lockset. You should be able to purchase the hardware and the lock/latch set at any decent window & door shop. They will lend/rent a jig to make it a simple job.

  • 1
    It may not be that simple. If you're going to switch to a bored (as opposed to mortise) lockset, you really should install an appropriate block of wood into the mortise first, to provide the structural support you are removing. And not everyone actually wants a "modern" knobset/lockset in an interior door; I'm quite fond of the glass doorknobs on my library's door.
    – keshlam
    Jan 8 at 4:22
  • The skill set necessary to properly plug a mortise lock hole in an existing door to a reasonable degree of "disappear" is actually fairly high and falls more into the "woodworker" skill set than "weekend warrior DIYer" skillset.
    – FreeMan
    Jan 8 at 13:53

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