This is the information I got from B&W when I asked the same question:
"Thank you for purchasing B&W! The midrange tension on your Nautilus 801s can be set by simply tightening the bolt to the point where there is some resistance, and adding another quarter turn to secure the bolt without over tightening it. If you set the midrange tension on your speakers accordingly, you should be fine."
"Thank you for purchasing B&W! The midrange tension on your Nautilus 801s can be set by simply tightening the bolt to the point where there is some resistance, and adding another quarter turn to secure the bolt without over tightening it. If you set the midrange tension on your speakers accordingly, you should be fine."