How this calculation works
Reading the head
Grade is stamped on the bolt head as radial lines. No lines is Grade 2. Three lines is Grade 5. Six lines is Grade 8. Stainless is usually marked with the alloy designation instead.
Higher grade means higher tensile strength, which means it can be torqued harder before it yields. A Grade 8 bolt torqued to a Grade 2 spec is barely holding anything. A Grade 2 bolt torqued to a Grade 8 spec will stretch and eventually snap.
Lubricated versus dry
The values on this page assume clean, lubricated threads. Torque is an indirect measurement — what you actually want is clamping force, and torque only gets you there by fighting friction along the way. Change the friction and the same torque produces a different clamp load.
Dry threads need roughly 25 to 30% more torque for the same clamping force. Run a lubricated bolt to a dry spec and you have overtightened it by that margin.
Where this does not apply
Electrical connections are a different animal. A busbar splice, a switchgear bolted connection or a transformer terminal is carrying current, and the torque value is about electrical contact resistance rather than mechanical holding force. Those specs come from the equipment manufacturer and are frequently lower than a mechanical spec for the same bolt size.
Structural steel connections are also outside this table — those follow AISC turn-of-nut or direct tension indicator methods, not a torque wrench value.
Use this table for hanging strut, mounting enclosures, securing equipment to a pad, and general bracket work. For anything carrying current or holding up a structure, go find the real spec.
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Frequently asked questions
How do I tell what grade a bolt is?
Radial lines on the head. No marks is Grade 2, three lines is Grade 5, six lines is Grade 8. Stainless carries an alloy stamp such as 18-8 or 316 rather than lines, and is generally weaker in tension than Grade 5 despite the corrosion resistance.
Do these values work for busbar connections?
No. Bolted electrical connections carry their own manufacturer torque values, aimed at contact resistance rather than mechanical clamping, and they are often lower than a mechanical spec for the same bolt. Use the value on the equipment or in its instructions.
Why does lubrication change the number?
Torque is a proxy for clamping force, and most of the torque you apply is spent overcoming thread and head friction rather than stretching the bolt. Lubrication cuts that friction, so more of your torque becomes clamp load. Dry threads need roughly 25 to 30% more torque for the same result.
Is stainless stronger than Grade 5?
Generally no. 18-8 stainless has good corrosion resistance but lower tensile strength than Grade 5 steel, which is why its torque values are lower. It also galls easily — stainless threads seize on each other under load, so anti-seize compound is worth using.
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nfpa.org for complete and authoritative code text. Always verify requirements with the code edition adopted by your jurisdiction and your Authority Having Jurisdiction (AHJ).