The two digits on a bolt head are not a part number. They are arithmetic — and once you know the rule you can read any bolt grade in the world.
IS 1367 sets the mechanical properties of threaded steel fasteners, aligned with ISO 898. The designation is a formula, not a catalogue code:
The first digit × 100 is the nominal tensile strength in MPa. The second digit is the yield as a percentage of that tensile. So class 4.6 means 400 MPa tensile and 0.6 × 400 = 240 MPa yield. Class 8.8 means 800 MPa tensile and 640 MPa yield. Once you have the rule you never need the table again.
| Property class | Nominal tensile strength | Yield / proof stress | Where it is used |
|---|---|---|---|
| 4.6 | 400 MPa | 240 MPa | General structural connections and light anchorage |
| 5.6 | 500 MPa | 300 MPa | Mid-range structural and foundation work |
| 8.8 | 800 MPa | 640 MPa | High-strength structural connections and heavy anchor bolts |
Yield for the higher classes is quoted as 0.2% proof stress rather than a lower yield point. Above class 8.8, hydrogen embrittlement risk in hot dip galvanizing rises sharply — that is a conversation to have before the order, not after the dip.
The practical problem that decides whether an assembly goes together on site.
Foundation and anchor bolts in property classes 4.6, 5.6 and 8.8, galvanized on our own line, supplied with our telecom towers, substation and transmission structures and heavy fabrications.
Pole line hardware and fittings are supplied on the same basis. Our range there is mixed — some items are manufactured at our Howrah works and some are supplied to the customer's specification and galvanized in-house. We state which is which on enquiry rather than leaving a buyer to assume.
Answered from our own line, not from the standard's cover page.
800 MPa nominal tensile strength, and a yield of 0.8 × 800 = 640 MPa. The first digit times 100 gives the tensile in MPa and the second digit gives yield as a fraction of it. The same rule reads 4.6 as 400/240 and 5.6 as 500/300.
Property classes 4.6, 5.6 and 8.8 for foundation and anchor bolts, galvanized in-house and supplied with our structures.
Usually the opposite problem — galvanized nuts are normally tapped oversize after coating to make room for the zinc on the bolt thread, so they can feel loose. If a nut will not go on at all, the bolt was probably galvanized to a structural coating weight rather than to ASTM A153.
Yes, routinely, to ASTM A153 with its embrittlement requirements. Above 8.8 the hydrogen embrittlement risk rises and the application needs discussing before the order.
No dedicated one. Cross arms are specified through IS 2062 for the steel and IS 808 for the section, with IS 2629 and IS 4759 for the galvanizing. Watch for specifications that cite IS 5561 here — that standard covers electric power connectors, not cross arms.
Tell us the standard, the coating requirement and the component, and we will confirm in writing what we can hold and how we will certify it. Galvanizing is on our own floor, so the answer comes from us and not from a sub-contractor.
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