sheared screw removal

[What's_nitro?]

This a 3mm screw? Is there any part of it protruding that you can get a hold of? If you have a dremel, you could try cutting a notch in it and then use a flat SD to back it out after it's heated. Other wise you'll most likely have to drill it out or buy a new castor block because there aren't any extractors that will work on screws smaller than 1/8".