How much weight can a 3/8 plastic drywall anchor carry? I want to mount a rear surround speakers ( appr. 8lbs ea.) to a spot where there just happens to be no stud.

 

You should be okay. That's a little heavy, but I have a couple of large framed items on my walls that weigh 6 or 7 pounds. There are several types of drywall anchors; you'll want ones that provide a backing action inside the wall rather than the simple plastic ones made for light-duty use. Check out the fastener section at the local home center.

 

Get what they call zip-its. Or sometimes called screw in anchors. They have a rating of 15 lbs and i've seen some up to 30 lbs.