Oddball screw size, door knob

[BFBOB]

I'm missing the setscrew from a door knob - one of those faceted glass knobs that were practically everywhere early last century.
It looked pretty big so I thought 1/4-20. But, no. wouldn't go in, and on closer look, the pitch is much finer than 20. OK, then it must be 1/4-28. No dice - slips in and out with no thread engagement at all.

Well, then, it must be bigger than 1/4 - 5/16? I found some 5/16-24's that I salvaged from some engine - size looked right, but the threads were too coarse. In desperation I hauled out my thread pitch gauges and determined the knob is 32 pitch, 5/16 diameter.

So far I've been unable to find any such beast - at least on ePay.

Any ideas? Or, anyone have an extra from their own (broken) door knobs?

(yeah, if I broke one I'd probably pitch the glass shards and save the rest)

 

[The Cobbler]

5/16-32 is schraeder tire valve size.

 

[MoToys]

Go to a locksmith with the knob. If he’s been around long enough he will have what you need.

 

[bonneyman]

Or take the part to your local hardware store. We had thread gauges of all sizes when I worked at Ace because so many people brought in items like yours needing a set screw or something.

 

[dogdog]

if it is closer to 1/4 size... I think 10-32 bolts 12-24 etc.. a lot of old hardware uses those threads...

M6-1.0 is also very close to 1/4-20 but they are probably not used in door knobs in the USA.

 

[dogdog]

https://www.engineeringtoolbox.com/us-machine-screw-diameters-d_1459.html

 

[Noworries]

Depending on the manufacturer (Corbin, Russwin) or if it is a cast iron lock body or a more modern steel body there really is no "industry standard" but try 5/16-24. There is also 2 different types of set screw that depends on the type of spindle the knob is going on. If you need more help message me with pics..

 

[JR 42]

It's almost certainly threaded into the base of the knob itself and looks like a set screw, not an oval headed screw.

I have no idea what the diameter or thread count is... any places nearby that sell salvaged building materials? The knobs themselves are valuable if they're in good shape. The place I used to work sold loose set screws from damaged knobs for $2 each.

 

[bob15]

McMaster Carr, 5/16, extra fine and make your own: https://www.mcmaster.com/screws/thread-size~5-16-32/

 

[BFBOB]

Bob15, yes, I looked at McMaster Carr. The only 5/16-32 they have is an odd critter made for a carbide tool bit holder. I could get one and modify it by cutting it in half - it's a thought.

But, it's so short that I wouldn't have enough meat to grind off the allen drive and cut a slotted drive. Am I being too picky?


yeah, probably.



then again, I could fire up the lathe and cut 32 pitch threads on 5/16 stock - but I've never been very good at thread cutting. Maybe it's time to learn.

 

[Hytekrednek]

can you drill and re tap for a more common fastener?

 

[MushCreek]

I just went through this restoring an old park bench. Approximately 17/32-13 threads on the stretcher rod. Since I had to make the stretcher anyway, I single-pointed threads to fit.

I used all antique glass knobs in my new house build. I'll take a look at them and see what they used.

 

[Jbullfrog]

Go to the hardware section of a building center, they have door knob stem and screw assortments. #12 was a common screw size that has been replaced in the last decade by 1/4"

 

[dscheidt]

The door knobs in my house are held in place with 9/32 x 28 screws. That's a standard size for certain parts in old singer sewing machines (singer had their own threads, and since they were vertically integrated, they hung on to them.) A local industrial sewing machine shop was able to supply me with some, once I figured out the part number for the set screw.

 

[bob15]

Bob15, yes, I looked at McMaster Carr. The only 5/16-32 they have is an odd critter made for a carbide tool bit holder. I could get one and modify it by cutting it in half - it's a thought.

But, it's so short that I wouldn't have enough meat to grind off the allen drive and cut a slotted drive. Am I being too picky?


yeah, probably.



then again, I could fire up the lathe and cut 32 pitch threads on 5/16 stock - but I've never been very good at thread cutting. Maybe it's time to learn.

For "only" 52 dollars you could get the 5/16-32 die from mcmaster instead of using a lathe

 

[Noworries]

For "only" 52 dollars you could get the 5/16-32 die from mcmaster instead of using a lathe

I'll say this again and I have 30 years experience as a locksmith... there is no industry standard it depends on the lock manufacturer and the most common is Corbin. They used 2 set screw sizes.. 1/4-20 and 5/16-24. It could even be metric if your lock is european...just saying

 

[jeffmoss26]

don't get me started on spindle threads...

 

[4xdog]

Did you find the setscrew you needed, BFBOB?

I ran across an old lockset cleaning out my parent's old house. I think I salvaged this one myself as a kid in the late 1960s-early 1970s. There are four doorknobs, and unfortunately the nicest glass one has gotten broken over the years. If this is from one of the two places I remember, it dates from the first quarter of the 20th C.

But it has a setscrew that's currently "surplus to needs".

 

[Two Sheds]

We have a bunch of the old octagonal glass doorknobs in our house, many of which were replaced with salvaged parts. Some have the 5/16-32 threads, and I gave up trying to find replacement setscrews for them. Most have 1/4-24 threads. I found that an M6 is close enough to fit in these.