Allen screw threads

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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Dave Taylor
I need to change out an allen screw for a slot or phillips.
How to find what thread it is?
1/16” allen key.


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yeah its hard to tell from the pic but its not an AN526-440 (or even a 632). Coarser.

This is a small cylinder that accepts an alternate air door control wire. When you want to pull the cowl, you must have a 1/16" allen key or you are sol. I am just trying to make everything on this airplane more manageable. Ideally a thumbscrew would work. Or a screw with a knurled end. No tools, just fingers. I could drill it and attach it to the device so you could always get it apart and it cant get lost.
Thanks POAers.
 
Wow, that looks really coarse for its diameter. If it is not 6-32 then something oddball. Fabricate your thumbscrew (i.e. grind the hex) and braze or epoxy it in?
 
Do you know a machinist? I'd measure the pitch with a thread gage. You could try measuring the threads per inch with a ruler but it's hard to do accurately on such a small fastener, especially with my aging eyes. You could also try this printable thread gage if your printer can do 1:1 fairly accurately.
 
Measure the OD of the screw itself. The size of the Allen key doesn't matter. Then measure the length and count the threads. How many will in in an inch?
 
Let'sgoflying! said:
How to find what thread it is?
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Find a thread pitch gauge--most tap & die sets have one. Determine which gauge fits your screw threads. Then measure the major diameter (across the threads) with a scale or micrometer.
 
You don't need a formal thread pitch set. Use standard bolts found in your junk box. For example if you think it might be 24 threads per inch, see if it fits next to a 3/8-24 bolt shank, which is a standard fine thread AN6 bolt. So is an AN5 which is 5/16-24 thread. Etc.........

I've never heard of a 6-24 thread, and metric threads are usually finer than coarse thread inch fasteners for the same diameter. Be careful though as metric threads are not as standard as you'd think.
 
That almost looks like something fabricated from a worm gear.

SUW_WormGearPair-1.jpg
 
cgrab said:
How does it hold anything together, it's just threads?
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It appears to be a dog-point set screw. Used to hold something in place. Like a collar on a shaft, etc. put a shallow round hole in the shaft, threaded hole in collar.
 
Grub screw, and there are 4 possible sizes. M3-.5, M4-.7, 5-40 and 6-32. To add to the number of variations, there are either 6 or 8 different point styles avaialble.
 
If you cannot locate a thumbscrew with that thread and do not want to braze/epoxy a thumbscrew to what you already have, you might be able to drill and tap a slightly larger size that you can find a thumbscrew for. You can also get a 6-32 heli-coil.
 
At the risk of being a Debbie Downer, you might not be able to get enough torque on a thumbscrew using just your fingers to properly secure a control cable for alt. air without putting a tool on it. In which case, you have gained little.
 
alfadog said:
At the risk of being a Debbie Downer, you might not be able to get enough torque on a thumbscrew using just your fingers to properly secure a control cable for alt. air without putting a tool on it. In which case, you have gained little.
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I dunno John, everyone has a pair of pliers but those 1/16" allen keys are a little harder to find.
I will let everyone know how it works out and why yet another of my ideas was awful!
 
Best is usually the easiest. go to ACE hardware they have a screw board. use it to find the size and threads, then buy the replacement.
and the Allen key to tighten it.
 
I am two days from removing the cowl; the suspense is killing me too - but I promise to report back!
 
6-32 won, btw.
I was wrong.
And I will need to shorten it.

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I would have handed it to 'Karl' the gunsmith and asked him what kind of thread it is. Would have taken him 30seconds.
 
Just did the drill today at the hardware store. It took a bit of searching. My other screw got a little buggered up.

It’s the ‘gas adjustment screw’ for the adjustable gas block on my PSA 18” Grendel Upper. For some reason I ended up with one, working out some minor bugs.
 
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