i'm looking to see if anyone have a link to a freewheel adapter that screw on to the freewheel treads. So it push the fixed cog or bmx freewheel and create a straight chainline. i saw it on ebay last week but couldn't find it. i have a hed disc w/ freewheel treads that i want to convert to a fix but the chainline will be way off without the adapter. also i'm think about having a machine shop machining a similar piece but with a reverse tread on the outside for the lockring. do you know how much does machine charge please help. thanks