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Truss rod wrench for O-Hole GJ?

GouchGouch New
edited May 2022 in Welcome Posts: 78

Greetings all (especially Luthiers)

I need to do some setup tweaks on an unbranded O-hole. The truss rod requires a 4mm allen ball-head wrench, and is adjustable through the oval soundhole. Distance from the northern top of the O-hole to the truss rod nut is 6”. No possible way can I get my gorilla-hand inside the soundhole, so I need something like an 8” 4mm angled wrench, or (possibly better) a 7 1/2” - 8” allen key that affixes to a fine-toothed ratchet.

Any tips for buying such a thing? Thanks in advance!

(I’m surely not the first person to need to do this, but it’s also not a hardware store item, and StewMac doesn’t have anything that meets my dimensional needs)


  • scotscot Virtuoso
    Posts: 620

    You can buy a variety of 1/4" drive hex key sockets in various lengths in metric or SAE from Snap-on or Matco, for $25-30 for each socket. These are excellent and durable mechanics tools, and great for engine or suspension work, but unnecessary for low-torque use. Buy a Cobalt 1/4" 4mm socket, a 4mm hex wrench, cut the short angle off with your cutoff wheel, figure the length you need (may require a 1"-3" extension to reach the bolt), lightly chamfer the business end (I don't like ball-ends) and epoxy the wrench into the socket. Over the years I've made many of these wrenches in various lengths and sizes for specific purposes when a store-bought one just wouldn't fit the needs of a job.

  • Posts: 4,239

    I see Stew Mac has 4mm truss rod wrench in 12" length. Is that too long?

    Every note wants to go somewhere-Kurt Rosenwinkel
  • GouchGouch New
    edited May 2022 Posts: 78


    This worked perfectly, got it on Amazon. From the ball tip to the T handle is just over 8”, and the T of the handle is fairly small and lands close to the center of the O-hole.

    Bondhus 75160 4mm ProHold Tip Ball End T-Handle w/ProGuard Finish, 220mm

    BucovanmalmsteenBill Da Costa WilliamsBones
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