JMIKS Fasteners supplies high tensile bolts, nuts, studs and special bolts in property classes 8.8, 10.9 and 12.9, from M3 to M36 and 1/4″ to 1-1/4″ BSW. Finishes are self colour (black), zinc plated and hot dip galvanized. We are a fastener wholesaler and supplier in Nava Odhav, Ahmedabad, since 2014.
High tensile bolts are medium carbon or alloy steel, hardened by quenching and tempered at 425 °C or more. This gives two to three times the tensile strength of a 4.6 mild steel bolt. ISO 898-1, adopted in India as IS 1367 (Part 3), sets the property classes: 8.8, 10.9 and 12.9 are high tensile, while 4.6 and 5.6 are mild steel.
In 10.9, the 10 means a nominal tensile (breaking) strength of 1000 MPa. The .9 means the nominal yield strength, where permanent stretch begins, is 90 % of that: 900 MPa. Our bolt grade chart explains every grade.
Minimum values from ISO 898-1, with mild steel 4.6 for comparison. The M20 column is the minimum breaking load of an M20 bolt (stress area 245 mm²).
| Property class | Steel and heat treatment | Min tensile strength | Min yield strength | Min breaking load, M20 | Matching nut class |
|---|---|---|---|---|---|
| 4.6 (mild steel) | Low or medium carbon steel, not hardened | 400 MPa | 240 MPa | 98 kN | 5 |
| 8.8 | Medium carbon or boron steel, quenched and tempered | 800 MPa up to M16, 830 MPa above | 640 MPa up to M16, 660 MPa above | 203 kN | 8 |
| 10.9 | Alloy or boron steel, quenched and tempered | 1040 MPa | 940 MPa | 255 kN | 10 |
| 12.9 | Alloy steel, quenched and tempered | 1220 MPa | 1100 MPa | 299 kN | 12 |
ISO 898-1 requires hex bolts and Allen cap screws from M5 upward to show the property class (8.8, 10.9 or 12.9) and the maker’s mark. Hex bolts carry it on top of the head; Allen cap screws on the top or side. Nuts show 8, 10 or 12 on a face or flat, or a clock-face code. B7 studs are stamped B7 on one end (ASTM A193). Never use an unmarked bolt where high tensile is specified.
A nut must be at least as strong as its bolt, or the thread strips. ISO 898-2 (IS 1367 Part 6) pairs class 8 nuts with 8.8 bolts, class 10 with 10.9 and class 12 with 12.9. A higher class nut suits a lower class bolt, never the reverse.
Keep one finish on bolt and nut. Hot dip galvanized (HDG) nuts are tapped oversize after galvanizing to clear the thick zinc, so an HDG bolt needs an HDG nut. A plain nut will not fit it, and an HDG nut on a plain bolt is loose.
Washers under high tensile bolts should be hardened steel: ISO 7089 hardness class 200 HV for bolts up to 8.8, and 300 HV up to 10.9. Friction grip (HSFG) joints use matched sets under IS 4000: IS 3757 bolts, IS 6623 nuts and IS 6649 washers. Spring washers add little locking on a tight high tensile bolt; a nylock nut works better.
Match the washer to the bolt. Use hardened washers under high tensile bolts, galvanized to match when the bolts are HDG. Our standard washers are stainless steel (SS 304, SS 316 and SS 202) for stainless joints. Hardened and HDG washers to match high tensile and HDG bolts are available on request. Avoid stainless washers under zinc coated bolts outdoors, because the zinc corrodes faster where the metals touch.
| Finish | What it is | Corrosion protection | Use it for | Grades |
|---|---|---|---|---|
| Self colour (black or plain) | No added coating: the dark oxide from heat treatment, usually lightly oiled | Low: rusts outdoors | Indoor machinery, oiled assemblies, parts to be painted | All, including 12.9 |
| Zinc plated | Electroplated zinc, typically 5 to 12 µm thick, bright silver, blue or yellow | Fair: indoors and under cover | Panels, machines, sheltered steelwork | 8.8; 10.9 only with baking after plating; 12.9 normally not |
| Hot dip galvanized (HDG) | Dipped in molten zinc at about 450 °C and spun; at least 40 µm locally and 50 µm on average (ISO 10684) | High: outdoors, wet and buried | Structural steel, PEB, towers, solar structures, foundations | 8.8 and 10.9, M8 and above; not 12.9 |
Why the limits? Acid cleaning and electroplating put hydrogen into steel, which can make very hard steel crack suddenly under load (hydrogen embrittlement). ISO 10684 covers hot dip galvanizing of bolts up to class 10.9 and nuts up to class 12, from M8 to M64. Class 12.9 is normally not galvanized or electroplated, and zinc plated 10.9 bolts should be baked after plating to drive the hydrogen out (embrittlement relief).
These items are listed in high tensile grades on our site. Most also come in mild steel 4.6 and in stainless steel.
| Product | High tensile grades | Metric sizes |
|---|---|---|
| Hex Bolt | 8.8, 10.9, 12.9 | M3 to M36, 6 to 250 mm long |
| Allen Cap Screw, Allen CSK Screw, Button Head Screw | 8.8, 10.9, 12.9 | M3 to M36, 6 to 250 mm long |
| Grub Screw | Sold in the trade as 8.8 to 12.9; the standard grades set screws by hardness (ISO 898-5), and steel socket grub screws are 45H | M3 to M36 |
| Hex Nut, Nylock Nut, Flange Nut, Lock Nut, Long Nut, Square Nut, Weld Nut | For 8.8, 10.9 and 12.9 bolts | M3 to M36 |
| J Bolt, L Bolt, U Bolt, Square Bolt, Step Bolt | 8.8, 10.9 | M6 to M36 |
| GI Threaded Rod | 8.8 | M6 to M36; 20 to 500 mm, or 1, 2 and 3 m rods |
| B7 & B8 Stud Bolt | B7, and L7 for low temperature | M6 to M36, 20 to 500 mm |
All also come in 1/4″ to 1-1/4″ BSW. B7 studs are quenched and tempered chromium-molybdenum steel with a minimum tensile strength of about 860 MPa up to 64 mm (ASTM A193), used with ASTM A194 grade 2H heavy hex nuts.
Always follow the class and finish on your drawing. Tightening values are in our bolt torque chart.
Yes. 8.8 is the first high tensile class in ISO 898-1: quenched and tempered steel with 800 MPa minimum tensile strength (830 MPa above M16) and 640 MPa yield. Classes 4.6 and 5.6 are mild steel.
Choose zinc plated for indoor and sheltered parts, where a thin bright coat is enough. Choose hot dip galvanized for outdoor, wet, buried and structural work, where the much thicker zinc lasts far longer. Use HDG nuts, tapped oversize, with HDG bolts.
Normally no. ISO 10684 covers hot dip galvanizing only up to class 10.9, and electroplating 12.9 steel risks hydrogen embrittlement. 12.9 bolts and Allen cap screws come in self colour, usually oiled. For outdoor joints, ask your designer whether hot dip galvanized 10.9 will do.
A class 10 nut to ISO 898-2, in the same finish. A class 12 nut also works; a class 8 nut can strip. With hot dip galvanized 10.9 bolts, use HDG class 10 nuts tapped oversize.
Send the product, size and length (for example M16 x 60), property class, finish, standard, quantity, and nuts and washers per bolt. A drawing or photo helps for J, L and U bolts.
Send your size, class, finish and quantity on WhatsApp +91 90333 11425, use our enquiry form, or download the catalogue (PDF). We reply within one working day, Monday to Saturday, 10 am to 8 pm.
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