Adjustable stem busted - Do I need to replace the whole stem? Today on my 2018 Pegasus Solero the adjustable stem broke. Probably due to overtightening of the righthand screw the nut at the left side of the stem tore free (see images).





The question is, whether I need to replace the whole stem or if there's a chance to buy only the nut somewhere. Also, how can I prevent this from happening again?
I'd call that part garbage, sorry.  You've overtightened it enough to tear apart the metal, and that toothed flange is probably custom.  

I would suggest replacing the whole unit with a different brand.  The one pictured APPEARS to be a threadless stem, but with the steerer clamp down below and the hinge/knuckle up on top somehow.  This is quite unusual.

Now that you know what kind of angle/length you prefer on your stem, consider purchasing one that fits those specs.  

A conventional non-adjustable stem might look more like this: