Why are some hex nuts blue in color?

blue-nut-galvanizedIt is often asked why some high strength hex nuts that are supplied with high strength bolts appear to be blue or some other color. This is normally the case with galvanized, high strength, heavy hex nuts and the reason for this is because of the wax lubricant applied to the nuts. According to the ASTM A563 specification, “Hot-dip and mechanically deposited zinc-coated Grade DH nuts shall be provided with an additional lubricant which shall be clean to the touch”. The dye color is so that the presence of the lubricant is obvious and recognizable. Supplementary Requirement S2 under ASTM A563 specifies that the lubricant shall have a contrasting color to make its presence obvious, however it is not required unless specified. Since the A563 specification only requires an additional lubricant for galvanized DH nuts, Supplementary Requirement S1 can be specified, which requires that the nuts shall be provided with an additional lubricant regardless of the finish.

When lubricated A563DH nuts are supplied, they will typically possess a contrasting color, most often blue, regardless of whether or not the supplementary requirement, S2, has been specified. This makes the lubrication easy to recognize and alleviates any potential confusion. Another thing to keep in mind is that ASTM A194 2H nuts may also come with a dyed lubricated coating. The reason for this is because the ASTM A563 specification allows for A194 2H nuts as an acceptable substitute for A563DH.

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    @Bill- Apologies, but we are not sure who is doing that. The nuts we typically buy are waxed by the manufacturers.

    @Abhishek- You should be able to purchase a wax or moly based lubricant at a local industrial supplier. Additionally, structural grade nuts like ASTM A563 DH will come already waxed.

    Hi, after doing this at multiple shops, here’s what I’ve found:
    1. CRC Heavy Duty Pro-Strength Degreaser – Best results. It sprays on, foams up, and lubricant comes off easily with manual wire brush. This will also remove the lubricant in the crevices. I bet spraying the foam plus pressure washing would also work.
    2. MEK and power wire brush – Second best results. Takes some time to remove the lubricant in the crevices and may need to supplement with manual wire brush or “flossing” with a rag.
    3. Pressure washing with hot water – Mixed results based on personnel. May take a while, may need to stand closer for a longer time. Beware that some galvanizing may be ripped off depending on your pressure, or surrounding paint.
    4. Savogran TSP (Trisodium Phosphate) – Worst results. Recommended by Federal Highway Administration. We sprayed this and let it soak for a while. It hardly came off with a wire brush or pressure washer. Other people must have had success; maybe we didn’t use it correctly. Maybe try with a power wire brush?

    Is there a standard for how long the color is to remain visible, especially after installation in the field? We have had some episodes where the bolts and nuts have “sat” in the field for a few weeks before installation and the color was gone. What should we be concerned about?
    Thank you

    @Tony- There are no standards for how long the wax must last once it is exposed to weather. The wax is typically water soluble, so it will deteriorate over time. The concern would be that if the wax itself has washed away, the nuts will not perform as well as they should – you will likely get some galling. If instead it is simply that the color that has faded, but the wax is still present, then my concern would be lessened.

    What about situations were the bolt must be turned from the head? The lack of lubrication between the head of the bolt and the washer greatly increases the torque required.

    @Joe- A great many factors can alter the torque needed to achieve tension, that is why torque should not be relied upon without verification. This is certainly one of those factors.


    @Bill- No, the blue wax should not make a difference. If it is on the top nut, then it will of course be out of the concrete, and if it is on the encased end, it only serves to hold the bolt in place, so you shouldn’t have any issues with waxed nuts.

    How can I obtain the wax with which to lubricate galvanized nuts when in a pinch? We are installing new steel columns on existing anchor bolts…

    @Chris – I don’t believe there is a standard or recommended wax – any stick wax obtained from your industrial supplier should be sufficient.

    What if I don’t know who manufactured the nuts? We need to clean the wax off before blasting and painting them. We have used pre-paint cleaner (Carboline Surface Cleaner 3) in conjunction with pressure washing, and MEK on a rag and still no luck getting the wax off. We had some luck using MEK while simultaneously scrubbing the nuts with a wire brush but it took a lot of effort, and with hundreds to do on a tight schedule we have to find another solution. I’m going to try Savogran TSP next! Has anyone else had luck?

    @Autumn- Apologies, but we have little to no experience removing the wax off of structural nuts. It is usually a water soluble, wax based formula, although it can vary by manufacturer. All structural nuts should be marked with the manufacturer’s ID (for example Nucor = n), so it should not be too difficult to find out who made them. If you’d like, we are happy to look at a photo and try to identify the manufacturer.

    As an inspector. What is the acceptable amount of blue? The bolts have been stored in kegs and dry but in a warm environment. 25% of bolt remains blue. I don’t know if this is the way they came or some melted.

    @Hugh- Normally speaking, bolts are not waxed, the nut is. If you are looking at waxed bolts, they must have been done special and there are no real standards to reference. As for the nuts, the amount is subjective. The A563 standard simply says that the wax must have a colored dye, it does not say how much color, how dark, etc. The purpose of the dye is so that the wax is visible. If you see enough color to know that the wax is present, then we’d say the nuts are acceptable.

    @Brandon- We don’t have any published recommendations, but as long as they are kept dry, several years should not be out of the range of possibility.

    @Don- Most wax on structural nuts is water soluble, so not only should it weather off over time, but you should be able to wash it off with water or a mild detergent and a little bit of scrubbing.

    @Terry- Most blue nut waxes are water soluble and will come off in time when exposed to the elements. If you need it removed quickly, you might need to contact the manufacturer and find out what kind of wax was used and what they recommend, since the type of wax can vary by manufacturer.

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