4mm Allen Nut Hot Rod Truss Rod

  • 97 Reviews
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12-1/4" overall length

Item # 2550
In stock, ready to ship!


6 or more $13.74
12 or more $12.95

14-1/4" overall length

Item # 2551
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6 or more $13.91
12 or more $13.11

18" overall length

Item # 2552
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6 or more $14.78
12 or more $13.93

24" overall length

Item # 2553
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6 or more $18.26
12 or more $17.21
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4mm Allen Nut Hot Rod Truss Rod

About This Item

A smaller 4mm (5/32") Allen nut for most instruments. Smooth two-way action corrects upbow and backbow, giving complete control over the neck.

Easy to install. The Hot Rod® fits in a straight channel. For proper operation, this truss rod must be installed so that the active rod (the rod with the adjustment nut) is below the passive rod. A wooden filler stick is not required.

Smooth 2-way action with superior strength for stubborn necks.
Our Hot Rod neck adjustment system features twin rods in threaded brass collars. The stainless steel active rod turns for smooth neck alignment, with 2-way action to correct upbow and backbow.

The Hot Rod requires an access cavity for the adjustment nut, and a straight 7/32"-wide x 7/16"-deep slot (measured from the bottom of the fretboard) for installation.

Pick the Hot Rod Truss Rod size you'll need:
(overall length includes the nut)

Resonator guitar
Acoustic guitar with 12th fret at the body
Acoustic guitar with 14th fret at the body
Electric guitar

We've designed the Router Bit for Hot Rod Truss Rods especially for routing your neck to fit our truss rods.


Product Instructions

Hot Rod Adjustable Truss Rods

Installation and adjustment instructions for Hot Rod Adjustable Truss Rod.

    • Item #
    • Weight
    • 2550
    • 0.197 lbs. (0.09 kg)
    • 2551
    • 0.232 lbs. (0.11 kg)
    • 2552
    • 0.296 lbs. (0.13 kg)
    • 2553
    • 0.385 lbs. (0.17 kg)

Customer Reviews

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  • 4.42 average rating from 97 reviews
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It Broke Again!

(Customer's Reviews)

OK - I had one of these break with the nut shearing off the rod while doing final set-up on the last guitar I built. StewMac was great about sending me a repair kit and they assured me that this issue was not unprecedented, but very rare. I like the design so I decided to take my chances and use one of these again.

Shame on me...The exact same failure happened again!! Looking at a my experience plus a couple of recent reviews with the exact same problem it looks like there was a bad batch from the manufacturer or something.

Stewmac has good stuff and I'll continue using them for a lot of other parts and tools, but I strongly advise that you do not buy this truss rod.


Best I ever used

(Customer's Reviews)

Been using these for over 15 years and never broke one. I produce a dozen acoustic guitars a year, and there's not a better truss rod out there for my guitars.



(Customer's Reviews)

the concept is a great one however i have sheered the nuts off of more than one of these. the metal is soft and what you would expect from a lower quality cast metal vs. a forged one. it would be nice to have a similar product with a detachable nut like the more traditional fender truss rods.



(Customer's Reviews)

Like the reviewer from NY, I was just about done with an acoustic guitar I am building for a customer, and the nut broke off of this truss rod while making adjustments. Very disappointing. Building a neck from scratch is a LOT of work, and for this to happen right at the end is very painful. I called StewMac and am hoping they have a solution that keeps me from scrapping this otherwise beautiful neck.


It Broke (part II)

(Customer's Reviews)

Ammendment to previous review, the product did break, but I got a call from Stewmac after I posted review with what sounds like a good fix for the problem and they're sending me the parts no charge, so despite having to do some extra work, I'm very happy with my customer experience.


It Broke!

(Customer's Reviews)

Used this product on my first build and it was easy enough to install after I rounded the edges of the metal blocks, but when I finally got near completion and string up the guitar to set the action, the threaded bolt sheared off about 1/4" from the nut. Not a case of excessive force, I have set up guitars before. Extremely disappointing as my first build is now stuck with backbow on the neck unless I do major guitar surgery to extract the broken rod and put in a new one.


The best.

(Customer's Reviews)

I honestly don't know of another truss rod like it. It's the fact that the two rods aren't welded together, but attached with those cool little nuts. The disadvantage is that it's big, but anybody that buys these ought to already understand that.


Work like a charm


I've built guitars with traditional truss rods and Hot Rod truss rods and I'll never do another traditional one unless a customer specifically asks for it. These work great and they're as easy to install as any others. As for others' comments about installing them wrong, well, the instructions are very clear: the adjuster goes on the bottom.

The 7/32" width is a bit of a pain because you either need to buy a 7/32" router bit or set up a jig for routing (which I've done). Feel free to reinvent this with a width of 3/16" or 1/4".

The depth is fine for the guitar and bass rods. My last build has a thin neck (15/16" from bottom of neck to top of fretboard at the nut) and I had no problems. I could see how they would be a bit deep for a banjo or mandolin though. You do need to take the truss rod into consideration in the design of the neck.


ok product

(Customer's Reviews)

Not super thrilled with these. Needs a thinner slot and also deeper than normal. Also possible to install these wrong if not paying attention. Due to the extra deep slot required and quirkiness, I usually get a truss rod from another supplier. Seriously if you are going for a thin neck I'd avoid this. Also prepare to buy the new router bit.


Used in 3/4 scale guitar

(Customer's Reviews)

Used two of these in 3/4 scale electrics. Have used the spoke nut hot rods in the last ~20 guitars and they have worked well. Can't think of a reason to try anything else but I needed something shorter. Worked great!

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StewMac PDF Catalog, page 74 See 4mm Allen Nut Hot Rod Truss Rod
on page 74 of our StewMac Catalog PDF

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  • Hot Rod® is a registered trademark of Stewart-MacDonald Manufacturing Company, Inc.