I simply want to share here that I’m an idiot because I stripped a stem bolt on my brand new bike, because I wanted to weigh the stem. A brand new torque wrench may also have been involved. I tried all the tricks I could find on youtube and - predictably - that’s rounded the bolt even more. Now I need to take it to the lbs to have it drilled out and I’m sad.
I’ve not done the stem bolt but I’ve done the crank arm bolts a few years back 
It might have been because I had no feeling in my fingers post treatment 
or I was simply over reliant and over enthusiastic on the then torque wrench.
Touch wood the only other bolts I’ve fully stripped are the tiny 2mm hex bolts (brakes pad holders and front mech) and I have managed to get them out with needle nose pliers or adjust cable length by hand by passing the ones on the front mech.
Glad to hear that this has happened to others too. 
I think my torque wrench is of the devil.
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It appears you did not strip the threads (either on the bolt or the stem), but rather rounded off the hex head. That’s pretty good news, as it’s easy to fix (a $15 screw extractor kit is all that’s needed). It also points to the culprit probably not being your torque wrench, but rather your hex bit. Cheap and/or worn-out hex bits should be kept well clear from bikes. Rounding off the head within torque wrench range is abnormal unless something is wrong with the bit itself.
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I think you’re right - the hex bits are the problem. The whole set was pretty cheap. I just ruined another couple of bolts simply by tightening them, but managed to get them out with pliers because they weren’t too tight. This has never happened to me before. I guess my torque wrench kit may have been a false economy.
The wrench itself is probably fine, it’s the bits that are a problem. Any hex wrench/bit that has a tendency to jam in the bolt heads should be rejected.
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Yes. Going to find myself a better set of hex bits. As for the bolt that is totally stuck, I don’t have the nerve to go near the new bike with power tools, so I’m booked in at the LBS.
Are you using Imperial or Metric hex wrenches? If you’re using Imperial, they’ll look and seem like they fit, but the tolerances will be slightly off and lead to rounding. Get a metric kit with millimeter bits rather than inch increments, if that’s the case.
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In simple cases, a bolt extractor can fit in the hex bolt head as-is and can take the bolt out without further work. Otherwise, the bolt needs to be drilled, and this should really be done on a press drill to prevent any damage to the adjacent parts. It’s a 3-minute job for anyone with access to a machine shop.
The MechEng in me cringed at that one. I hope you throw the torx bit in the bin afterwards, to prevent moving the problem onwards to some other object down the line?
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I have all metric bits, but they are pretty budget. However, I just located a bunch of really good quality hex bits among my power drill bits. I wish I’d used those all along.
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I tried to glue a disposable allen key into the rounded bolt with gorilla glue (saw this in a Youtube video), but it didn’t work.
Probably better with an epoxy (J-B Weld) than a glue, this stuff (and the like) creates a ridiculously strong bond:
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Since everyone is being so helpful here, could I get some advice on what I did with a disk brake adapter? I’m totally new to disc brakes, so just feeling my way. I got a second wheel set that I want to keep ready for use so got a cassette and rotors to put on. The adapters look different though. Did I do it right? Top is wheel as delivered, bottom is the adapter that I put on the spare wheelset.
I’m going to go out on a limb here and reveal that I never use a torque wrench anymore. Why? Because I’ve been building bikes since I was 8 years old and doing serious road riding since I got my first good bike, a Raleigh Super Course, at 13. I’m 55 now. I’ve always been a DIYer.
I just never had a problem before torque wrenches were a thing and still don’t have a problem.
One thing people forget is that often it says “6nm max”. It doesn’t say to torque to 6nm but somewhere below. Basically that means tight enough for the job but don’t over do it. I can get that by hand.
I bought have a 5nm torque key a while back for stems because I thought I’d get more modern. I torqued a stem bolt with it and my first thought was damn, that is a lot of torque, way tighter than I was comfortable with on a stem.
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mate 
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I have several, and use them most of the time, however a torque wrench is just an indicator of torque, and is subject to being ‘off’. I had a cheap Craftsman wrench, and it was not meant to be very accurate in the beginning, and just got progressively worse over the years. It’s also famous for not being rebuildable, and able to be recertified.
I buy brand name torque wrenches, and own several from CDI. And owners need to treat them properly too. Dial them down to the lowest setting after use, and also use your ‘feel’ to get an idea if the wrench is off. If it feels like too much torque, it could be. Also having a torque wrench rebuilt and certified is not inexpensive. I’d never done it until one of my CDI wrenches felt off. It was. The cost of the rebuild was just under buying a new one.
And, as others have said, the quality of the bits/tools are very important. I have been disappointed in the quality of recent Park Tool allen tools. I stripped a crank arm bolt head using a Park Tool allen wrench. They used to be the definition of quality. Sad to see them sliding… And the Torx key/bit trick does work. Not every time, but it can save your butt in many cases.
Torque safe…
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Looks like the first wheel is a ‘six-bolt hub’, and the second is a Center Lock hub, with an adapter?
It should all be good. Just realize that you may have to recenter the calipers every time you change wheels. The easiest way is to get a centering tool, and use it and an allen wrench to loosen the caliper and reset center. It’s a great time to check for true of the rotor as they can get banged around off the bike. Pad contamination can be an issue too, but I have three wheels for one bike, and switch them fairly often. It’s amazing how quickly I can recenter the calipers, and the rear seems to be the finicky one for some reason.
I have this one, but there are many out there. (And keep it clean too) After you have done it a few times, you might be able to skip using the tool. You may also luck out, and not need to adjust things. One wheel is off enough I have to adjust the caliper.