The Importance of a Snug Wrench

If you’ve read Sketchy Setups, you’ll probably have spotted that I mention the importance of using the right sized wrench for adjusting your truss rod.

Well, let me just mention it again:


Seriously. Really important.

This is especially true of guitars and basses that use an hex/allen wrench.

You know these wrenches - they’re hexagonal rods with a 90-degree bend. They slot into a hex socket in the truss rod adjustment. Simple and effective.

The problem, however comes from using a wrench that’s just a little too small.

In technical terms, the pointy bits on the wrench don’t sit snuggly in the pointy bits on the adjustment (stop me if I'm going too fast). ;-)

This ‘mismatch’ can cause wear inside the hex socket and, if you’re not careful, you can end up with a round socket instead of a hexagonal one. It doesn’t take an engineer to work out that a round socket probably isn’t going to work so well.

Fender truss rod nuts are particularly prone to wear

So then, if you’re adjusting anything that requires an allen wrench, use the right size. This goes for Fender-style saddle height screws and especially for truss rods.

Safety Precautions for Allen/Hex Wrenches

  • Don’t use metric wrenches for imperial sockets or vice versa. There might be only a tiny difference in size but it might be enough to cause problems.
  • Don’t use worn wrenches.
  • Cheap wrenches can sometimes be made to poor tolerances. Make sure your wrench feels snug.
  • Cheap wrenches can be softer. When they start wearing, they can wear the socket too.
  • Insert the wrench as far as you can into the socket — the farther in, the better the ‘grip’.
  • If a wrench slips as you turn it, stop and regroup. Make sure you’ve got the correct size and if the next size up is too big, your wrench might be incorrect or worn.
    Or the socket might be worn, in which case you may have a bigger job on your hands.

If you can, get a decent set of both metric and imperial allen wrenches. They’re not terribly expensive (although don’t buy the cheapest ones you can find). A set of each will leave you well equipped for your setups.

Get a Grip

Stew Mac offers a ‘Gripper’ wrench. This has a hex head that tapers — it gets wider along its length. The idea is that, as it’s inserted, the wider part might be enough to grip the socket.

They’re not for everyday use but it might just get you out of a jam. However, if your adjustment nut has started to wear enough that a standard wrench won’t grip, I’d really recommend replacing it. Use the Gripper wrench to remove the nut and install a new one. Otherwise, you risk wearing the nut to the point where even the Gripper won’t work.

The Bottom Line

Yes, I really did write an entire post about allen wrenches.

Yes, I think it’s that important. I see too many guitars with stripped truss rod adjusters. While I’m glad of the money, I’d be happy seeing fewer. ;-)