IS 1363 Part 1 : 2002Hexagon Head Bolts, Screws and Nuts of Product Grade C - Part 1: Hexagon Head Bolts (Size Range M 5 to M 64)

IS 1363 Part 1:2002 is the specification for hexagon-head bolts of product grade C, sizes M5–M64 — the dimensional standard for the common, lower-precision (grade C) hexagon bolts used widely in general steel construction, fixings and non-precision bolted connections. Dimensions here; the mechanical property classes (the structural strength) are governed by IS 1367.

It sits in the fastener stack:

• IS 1367 Part 3 / Part 5 — mechanical properties of bolts / nuts (the *strength*) · IS 1364 Part 1 — product grade A & B (higher precision) hex bolts
• IS 800 — steel design (bolted connection design) · IS 816 — welding (the alternative connection)

The single most important thing about IS 1363 Part 1 is that it fixes dimensions and product grade (tolerance class), not strength:

• Product grade C = the coarser tolerance / general-purpose class (vs the tighter grades A/B in IS 1364) — appropriate for ordinary fixings and clearance-hole connections, not precision or slip-critical work
• Size range M5–M64, head/thread/shank dimensions and tolerances — so bolts, nuts and spanners interchange
• Strength is separate: the property class (e.g. 4.6, 8.8, 10.9) per IS 1367 Part 3 is what the IS 800 connection design relies on — a structural bolt specification is size + product grade + property class, all three

The engineering point: specifying a bolt by size alone (or assuming 'a grade-C bolt' implies a strength) is the classic error — IS 1363 Part 1 gives the *geometry/tolerance*, and the load-carrying capacity comes from the IS 1367 property class. A grade-C dimension with an unspecified/low property class is a connection of unknown strength.

Scenario: an ordinary (non-slip-critical) bolted steel connection designed to IS 800.

Step 1 — design demand: IS 800 gives the required bolt size and property class (e.g. M20 grade 8.8) for shear/bearing/tension.

Step 2 — specify completely: bolt to IS 1363 Part 1 (product grade C, size) *plus* the IS 1367 Part 3 property class *plus* matching IS 1367 Part 5 nut — geometry *and* strength.

Step 3 — suitability of grade C: confirm grade-C tolerance is acceptable (clearance-hole, non-precision); precision/fitted/slip-critical work needs grade A/B (IS 1364) and the appropriate procedure.

Step 4 — matched assembly: bolt + nut + (washer) of compatible class; correct tightening per the connection type.

Step 5 — verify on delivery: size, product grade and property-class marking on the bolt head.

Specified as size + product grade + property class with a matched nut, the connection carries the design force; specified by size alone it is a fastener of unknown strength.

1. Specifying bolts by size only. Size + product grade + property class (IS 1367) together define a structural bolt — size alone is incomplete.

2. Confusing product grade with strength class. Grade C is a tolerance class, not a strength — strength is the IS 1367 property class (4.6/8.8/10.9).

3. Using grade C for precision/slip-critical work. Coarse-tolerance grade C is for general fixings; fitted/precision needs grade A/B (IS 1364).

4. Mismatched nut. Pair with the correct IS 1367 Part 5 nut class — a weak nut defeats a strong bolt.

5. No property-class verification. Check the head marking — unmarked/wrong class = unknown capacity.

• IS 1367 Part 3 — mechanical properties of bolts (the *strength* class) · IS 1367 Part 5 — nut proof-load properties
• IS 1364 Part 1 — product grade A & B hex bolts (precision) · IS 800 — bolted-connection design
• IS 816 — welding (alternative connection) · IS 2062 — structural steel (the connected members)

IS 1363 Part 1 is reaffirmed and its core lesson is a definitional one engineers get wrong constantly: it specifies **bolt dimensions and product (tolerance) grade — *not* strength. 'Grade C' is the coarse-tolerance, general-purpose geometry class; the load capacity comes entirely from the IS 1367 Part 3 property class (4.6/8.8/10.9), and a complete structural bolt spec is size + product grade + property class + matched nut**. The recurring failures are specifying bolts by size alone, conflating product grade with strength class, using coarse grade C where fitted/slip-critical precision was required, and pairing a strong bolt with a weak nut. Treat the bolted connection as a designed assembly per IS 800 — specify all three attributes, match the nut (IS 1367 Part 5), and verify the property-class marking — and it carries the design load; treat 'a bolt' as a commodity and the connection strength is unknown.