I am trying to hang a TV mount into the wall studs above a fireplace. The hex cap screws that came with the mount don't fit snugly into the 7/16" nut driver bit and are too big for the 3/8" bit. There is no way I can use a manual hex head screwdriver to get these things into the wall. I need to use my drill.

Did I buy the correct attachment to use my drill to get these screws into the stud? Or, is it possible the hex cap screws that came with the mount are not "to industry standard measurement." BTW - I took a ruler to the hex cap and sure enough, it measures 3/8".

Where am I going wrong?

  • 7
    Maybe they are metric sized hex heads? 3/8" is between 6 and 7 mm, and 7/16" is between 5 and 6 mm. I suspect you need a 6 mm nut driver.
    – wallyk
    Commented Aug 25, 2013 at 22:22
  • 1
    @wallyk Almost all TV mounts use metric sizes (possibly because the bolts into the TV are standardized for metric). wallyk is probably right.
    – bib
    Commented Aug 26, 2013 at 11:44
  • 2
    Side note: When driving lag screws for television mounts, I often find that a ratcheting socket wrench is the best tool for the job. A nut driver simply does not offer enough torque. A portable drill motor can also lack the required power for the job, though a drill motor with a impact feature often works a bit better.
    – Tester101
    Commented Aug 26, 2013 at 12:48
  • @Tester101 Agreed on socket wrench, though if you want to go the power tool way, an impact driver is the correct tool. While I guess it might be possible with a hammer drill, it's probably due to brute force as hammer drills drive the bit forwards, and I'd be worried that it makes the screw loose around the threads more than anything. Impact drivers apply additional torque, which is what's needed here.
    – gregmac
    Commented Aug 26, 2013 at 14:09
  • 1
    @gregmac I didn't mean to imply using a hammer drill. My drill motor has an optional "hammer" feature, that can be engaged and disengaged. This feature mimics an impact driver, adding a smack in the direction of rotation.
    – Tester101
    Commented Aug 26, 2013 at 14:16

1 Answer 1


The DeWalt nut drivers (and others also) are very shallow (only meant for driving sheet metal screws (and are magnetic).

As suggested, regular sockets with a rachet handle will cover the hex head and not be pushed-off by the cap head.

You can get a socket adapter for your impact driver and then use your regular sockets: enter image description here

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