How do I remove parts from my 3d printing file? I have purchased a 3d model online in the form of stl files.
It all printed really well apart from one part. The hook shaped part at the front of the image.

I can't work out how to delete the other three objects from the file so I can print out only the part I need. 
I've tried selecting in edit and deleting but it seems to leave a cloud of undeleted bits.
Any help would be much appreciated!
Rob
select vertex of part you want to keep
select linked by L
invert selection Ctrl+i
delete X