When I first got my roller, both normal and recessed connectors had bad threading. I had to try to get rid of the burrs by using an old cartomizer, pulling as I screwed in and pushing while I screwed it out( with the connectors off the roller of course.) I contacted Atimzoo and they were kind enough to send me out new connectors that worked perfect.
7mm x .5 High Speed Steel Plug Tap - Amazon.com
Currently out of stock but they do replenish on a reg basis.