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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14 comments

    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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