Foundation bolts hold steel columns, machines and poles down to concrete. This guide covers the types, the Indian standard, grades, setting and ordering. JMIKS Fasteners supplies J bolts, L bolts and U bolts from Ahmedabad.
A foundation bolt, or cast-in anchor bolt, is fixed in position before the concrete is poured. Its lower end is hooked, bent or fitted with a plate, so it cannot pull out once the concrete sets. The threaded top projects above the concrete and takes the base plate, washers and nuts.
The Indian standard is IS 5624 (2021 revision). It covers cast-in bolts set before concreting and shows several anchoring shapes, including the J hook. Your structural drawing gives the exact type, size and grade.
JMIKS supplies J bolts and L bolts in sizes M6 to M36 and ¼” to 1-1/4″ BSW, in the length shown on your drawing.
| Grade | Material | Typical use |
|---|---|---|
| 4.6 / 5.6 | Mild steel, 400 / 500 MPa tensile strength | General foundations, sheds and light structures |
| 8.8 / 10.9 | High tensile steel, hardened and tempered, 800 / 1000 MPa | Heavy columns, machinery and towers |
| SS 304 / SS 316 | Stainless steel | Wet, coastal or chemical areas |
| SS 202 | Lower-nickel stainless steel | Dry, indoor use |
Finishes are self colour (plain), zinc plated and hot dip galvanized (HDG). Zinc plating suits indoor or covered work; for outdoor and buried use, mild steel foundation bolts are usually hot dip galvanized. Match the nut class to the bolt: class 5 for 4.6 and 5.6, class 8 for 8.8 and class 10 for 10.9 (ISO 898-2). See our bolt grade chart.
Example: an M24 bolt with 40 mm of grout, a 20 mm base plate, a 4 mm washer (DIN 125), a 21.5 mm nut (ISO 4032) and three threads at 3 mm pitch needs 40 + 20 + 4 + 21.5 + 9 = 94.5 mm, so about 95 mm of projection.
A sketch helps: JMIKS quotes against your sketch or drawing.
Foundation bolts are cast in with the concrete and must be set out accurately in advance; they suit heavy, planned loads such as columns and machines. Anchor fasteners, such as wedge and sleeve anchors, are post-installed in holes drilled in hardened concrete, for fixings added later. Do not swap one for the other without the engineer’s agreement.
Both are bent foundation bolts and hold in concrete in the same way. A J bolt has a curved hook and an L bolt has a 90° bend. Use the type shown on your drawing.
It depends on the bolt size, the load and the concrete grade, and is set by the structural engineer. Follow the drawing.
Mild steel 4.6 or 5.6 suits general foundations and light structures. High tensile 8.8 or 10.9 is used for heavy columns, machinery and towers. SS 304 or SS 316 suits wet, coastal and chemical sites.
For outdoor and buried use, mild steel foundation bolts are usually hot dip galvanized. Use HDG nuts with HDG bolts, because the nuts are tapped oversize to fit the coating.
Send your sketch or drawing, grade, finish and quantity. Message us on WhatsApp at +91 90333 11425 or use our enquiry form, and we reply within one working day. See the full range in our catalogue (PDF).
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