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I have a question about hex key/ Allen key / Allen Wrench and Screws.

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I have a question about hex key/ Allen key / Allen Wrench and Screws.

Old 06-02-2015, 06:49 AM
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Default I have a question about hex key/ Allen key / Allen Wrench and Screws.

I don't know how to measure the size of a Hex socket (Allen). I wish I did because normally all I got to go on is what it says on the package. The problem is sometimes I get things that come with them in and if one gets lost, I got to replace it. But replace it with what? I have a pack of used and new ones that have been in things. In the past I always just put one of these tiny ones on a wrench and carefully try it. Figuring out what thread works this way isn't too hard for me. But sometimes when I'm working with some really tiny screws, the wrench it's self gets caught in the screw socket. I try not to over tighten these things, and yet you need to have them tight enough so that they don't come out. The tiny one's I'm talking about is the ones that are often used in wheel collars on 40-90 size planes. I have a pair of retracts that holds the struts in with two tiny Allen set screws. It is important to me that these don't come out during flight. But when I want to tighten them down the tiny Allen wrench will start to slip inside of the screw. Since they are so tiny it is hard to see why. The Allen Wrench feels like it is the right size. I think what happens is the Allen wrench gets a little rounded on the edges allowing it to turn slightly in the socket. I find this odd because I don't think I was the one who over turned the Allen Wrench. The other problem I have is Metric verses American. Besides a set of wrenches I bought on purpose, I couldn't tell you what the other ones are that came in some of my airplane kits. Once again I have to go on how they feel. This has been a very annoying problem. I'm posting this to see if any of the other modeller's out there have any tips or tricks on how to deal with this issue. I would be fine with buying new sets if only I knew how to figure out what I needed. I think over 90 percent of what I have came with kits etc.

*Note: I use Loctite on important screw threads.

Last edited by gregoryshock; 06-02-2015 at 06:52 AM.
Old 06-02-2015, 10:32 AM
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Greg the majority of the hardware used in current arf's is metric keeping in mind for that tiny stuff some of the metrics are also half size increments, i.e. 5mm 5.5 mm 6mm and so on.

Now if you really want to free yourself from trouble with wheels, anyway I find that soldering axles to be a far better way without much bother.


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Old 06-02-2015, 10:34 AM
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I don't use loctite but grind a flat spot where the screw bottoms out on the wire. As to the size?? I have never measured but I have taken several of my missing screw collars to a special hardware store I go to once in a while and test fit screws until I find the ones that fit the different size collars.
Slipping is usually the wrench has rounded a bit, when this happens I just grind off the worn part and have a new wrench. To fit a wrench I just find the wrench that doesn't wobble inside the set screw.
Other then that most the screws used on our planes are either 2-56 or 4-40 and I just know what wrench it is that I need for these two sizes. I buy these screws in bags of 100 from Micro Fastener. I can get them at that super hardware store but they stock high grade and charge accordingly, like too much. You don't need grade 8 for much on a model plane.
Old 06-02-2015, 08:32 PM
Tom Nied
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I used to be anal about this. And I think it came from when I first started flying CL in the late '60's and using wheel collars and having wheels come off in flight. Hated that. Progressed to the soldered washer to hold the wheel on, great but not so great for the plastic hub. Went back to the wheel collar that I would epoxy on the axle as well as the set screw. Those wouldn't come off for anything. Finally arrived at the file a flat and snug down the set screw with thread locker. Works like a charm. With the flat they wont slide off and thread locker prevents the set screw from loosening. You don't have to make the set screw so tight that it indents the axle, just snug. If you ever have to get it off, just heat it up with a soldering iron and the thread locker loosens and you can get it off. At least this is what is working for me. Now, I wish DuBro would make a light collar out of the same material props are being made of. I think it would work just fine.

Last edited by Tom Nied; 06-02-2015 at 08:40 PM. Reason: spelling
Old 06-03-2015, 06:03 AM
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These little allen wrenches slip. You can't do anything about it. Allen wrenches are inherently prone to slipping because you don't have any 90 degree surfaces to bear the load like with a Philips or flat screwdriver. And the wrenches supplied with packages of wheel collars aren't the best quality to begin with. Tom's method is the right way; grind a flat where the set screw needs to go, put a drop of loctite on it, then snug it down. Even if it were to work loose 1/2 a turn or so, it would still hold just fine.

And for your original question, if you stick the allen wrench in the socket and it doesn't wobble, it's the right size.

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