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Door Knobs for Small Bore Hole 1-1/2 Inch to 1-3/4 Inch

A common request we get around our shop is for door knobs or levers made for the small 1-1/2" or 1-5/8" bore hole. Actually, while there are deadbolts available that are made specifically for the smaller bore, today's knob and lever sets are, for the most part, made to fit the standard 2-1/8" door preparation. There are a few exceptions, and we'll discuss those here in a bit, but there are no door knobs or levers made for the 1-5/8" bore. There are, however some hardware sets that will easily work on the smaller door prep with a little help, even though they're not specifically made to fit the smaller bore.

The problem: Chances are if you're reading this article, you've got doors with the smaller bore hole. You have probably even been to your local home improvement store and bought replacement door knobs only to find that they wont fit in the hole. The Schlage and Kwikset hardware you will find at the home improvement store will all have a cast aluminum insert that requires the hole be drilled to 2-1/8"(see image). If this is the hardware you want to use then about the only option is to cut the hole to 2-1/8. This is a little bit of a challenge, but if you've got some skills and a few tools it can be done. Because the hole is already dilled at 1-5/8" its tough to re-drill it bigger since hole saws require a pilot bit to keep them centered and cutting straight. You can still do it, but you will need some kind of solid jig clamped to the door to keep the hole saw where you need it. If you're only doing one door, you could carefully cut the hole a little bigger with a jigsaw, but thats a pretty time consuming way to do it.

The Solution: If you get a knob set that doesn't have the little metal insert piece, its pretty easy to install on a wood or metal door with the 1-1/2" or 1-5/8" bore. Look at the inside of the SureLoc door knob at the right here. There are just two threaded posts that pass through the door. These are spaced at 1-3/4" so its really not much wider than our bore hole. The only trimming you will need to do is right where the two threaded posts pass through the door. The easiest way ive found to trim for the posts is with a round rasp or file. Just mark the center line on the bore hole and file away at the wood or metal there until the threaded posts can be inserted into the bore. A wood rasp removes the material quickly. You can file out enough space in just a few seconds. For metal doors use a round file, it will take a little longer on the metal door, but its still not a big deal. The threaded posts on an Emtek knob or lever are in the verticle position so you will file out a little spot at the top and bottom of the bore hole rather than the sides on one of those.

Once you get the sides of the hole filed out enough test fit the outside half of the lockset. If it seems to fit into the bore ok go ahead and install the latch into the edge of the door. You may need to drill the cross bore (hole for the latch) deeper. The latches were designed for use with doors that have a 2 1/8" dia. bore hole. So if yours is much smaller, the cross bore will not be deep enough. Once the latch is in place, go ahead and install the knob and tighten the through bolts and youre done! Really not difficult at all.

Not all doorknob or lever sets are made for the 2-1/8" bore hole. There are some, like the Baldwin Estate Series hardware that use a small 3/4" bore hole. If your bore hole is as small as 3/4", give us a call and we can help you find a lock that will fit your door. Also, Mortise locksets dont really have a bore hole like the tubular sets do. You can recognize a mortise set by the tall faceplate on the edge of the door.

 

  schlage doorknob interior component
The cast zinc housing on most popular door hardware, like the Schlage lock here, requires a 2-1/8" bore hole.
door knobs without the cast ionser piece will fit with minimal trimming
If you have the small bore door preparation the easiest solution is to use a lockset that just has the screw posts like this SureLoc doorknob. Other hardware sets with this type of mounting are Emtek, MaxGrade residential, EZSet residential and Dexter. The bore hole can be trimmed slightly to accept the two threaded posts shown above. (Emtek sets come with a plastic latch alignment piece - this piece would have to be left out for installation on small bore hole).
Use a rasp to remove a little material inside the bore
To make a little room for the threaded posts for the doorknob mounting I used a round rasp on this wood door. You could also just ream it out with a drill bit or a blade of some kind - jigsaw or sawzall. On a steel door use a round file.
install the latch and complete the doorknob installation
Once the sides are trimmed a bit with the rasp the lockset slides right in and installs without any problem. Some hardware sets, like the Emtek, have the threaded posts top and bottom instead of on the sides, but its pretty much the same procedure for those.

Please keep in mind that we cannot guarantee fitment on everything. We've heard of all kinds of weird door preps over the years and there is just no way for us to be able to know and see what you have exactly.

 

 

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