rounded hex rear bolt 379 wont unscrew


My bolt 379 with hex hole head is now rounded (the one that keeps the metal for magnet), after many times mount/unmount.
It has unscrew red glue on it, since last time. I had mounted it with 2 Nm torque.

It can not unscrew! The tool turns inside the rounded hole (no more hex).

What to do to unscrew it?


Hi Alex,

you should not use the red glue - instead of take the blue quality.

To open red glued bolts there is only one chance; heat it up!
(Unwanted side effect - the plastic washers will melt.)

Edit: Sorry, forget that thing with the magnet as it is at the front.



I thought red and blue are the same… wrongly so.

I heated it with hair dryer. It’s now so hot I can not touch it.

YEt it does not unscrew. The hole is now almost perfect round.

If I unscrew the other (right) bolt - will it work?


Ah I see - you need also to cut a slot in the bolt’s head; perhaps by using a very small grinding disc (you do know “Dremel” tools?).

Hairdryers are most likely not hot enough, try a heatgun or a small blow torch.

No, unsrcewing the bolt 373 at the opposite side doesn’t help at all.
(This way you can just remove the bottom tube from the axle, but the axle is screwed into the seat tube from the left side.)

Thanks for indications, i’ll go search for dremel and heatgun tools at shop.

No experienced bike/car workshop in reach?
They may have all the tools already.

Edit: Jfyi



I want to thank you very much - it worked.

The dremel worked very well, but had to pay great deal of attention in cutting: added light, glasses, etc. Then I tried to unscrew but it would not turn, and would damage the head further. So I had to apply the handgun at 650 degrees Celsius, for about 2 min (just 1 min would not work). Then it smelled plastic. And then I tried the screwdriver and it turned. Not easily, but it turned. I removed the bolt. I was so happy that I forgot to remove the wheel. So the plastic cooled and I could not remove the wheel. SO I applied again the handgun until plastic smell, and the wheel could be removed easily.

I took photos of the equipment and bolt, before after. But dont know how to put figures… I will check it soon.

Again, thank you very much. It was the right advice. The operation took only a few minutes and no frustration.


PS: thank you for the explanation of red/blue. The glue I used is not loctite but some other brand - Ront Production. It is red color and it says indeed ‘strong’ (fort, in French); they also offer a green version, dubbed ‘medium’ (resistance moyenne). In both the glue color is red. The green and red indications are printed on the description text. It is very confusing.

The replacement bolts I ordered by chance (I apply a major rehaul for other pieces on the bike) from came with a blue stain on them; I will just rely on that and not add any more glue.

Hi Alex,

thank you very much for your feedback!
I’m very happy that you could solve the problem. :smiley:




Yes, that blue thing on the original bolts should work of course without additional glue.