Strange Sized Hex/Allen Key

24 Jun 2008
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United Kingdom
I am trying to replace a part on my shower - should be a very simple job, but it's turning out to be a complete nightmare.

The problem is that all of the parts of the shower are held in place by hex screws that none of my hex keys fit. I have full standard metric and imperial sets so there shouldn't be a problem but the 2mm metric key is too small and the 3/32 inch imperial key (which translates to 2.38mm) is too large.

To make things even stranger, the spare part I bought from the manufacturer has a new hex screw for fitting the part and the 2.5mm key fits it without any problem.

Does anyone have any idea what is going on here or how I can get this part fitted? Is there an obscure size of hex key available that will fit these screws or have the screws shrunk in the shower!? (only half kidding!).

Could I take a drastic measure and forcibly remove/drill out the screw that is holding the part in place (I only need to remove one screw and I could use the replacement that came with the spare).

Not sure if this is a good idea, but I really need to get this fixed so any help you can give would be greatly appreciated.
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have you tried hammering in the one that seems too tight? allen keys are cheap so maybe you could grind a slight taper on it.

A left handed drill/screw extractor tool will probably do it (on very low speed). they are not brittle steel like the ironically named easy-outs, but like a HSS drill. If you use one the size of the screw, and end up drilling its head off, you can probably take the cover off and perhaps wind out the stub with a mole?
Thanks John. I'll try hammering in the allen key and see if that helps.

If it doesn't work I might get back to you about the option of extracting the screw - it sounds tricky so I think I'd need some further advice on that!
Have you tried wedging a flat blade screwdriver in the key socket between 2 "points" and unscrewing it like that?
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nos - JohnD's advice is the way to go but tapping an allen key (especially a small size) in can sometimes be awkward as you are forced to hammer (tap) against the right-angled section - this often causes 'bounce' resulting in slippage. If this is a problem modify the key by cutting off the right-anged section (grind or nip-off with pliers/cutter - small key should snip off OK) then you will have created a 'punch' which will drive into the hex socket; apply mole grips to undo. Then replace modified allen key with a new one to make-up your set.
Thanks for all the great advice. I ended up using a hacksaw blade to cut a slot then used a normal screwdriver to take out the screw.

After getting the screw out and having a good look at it, it turned out that it was not a "strange sized hex screw", but a torx screw. Very difficult to spot for amateurs like me!

Well you live and you learn and I've got my shower fixed now.

Thanks again for your advice.


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