Free tool · Welding and fixings
Bolt and Fixing Guide
Pick a size and class: clearance hole, edge and pitch distances to BS EN 1993-1-8, and indicative tightening torques, with every number sourced.
Quick answer
Choose a metric bolt from M3 to M33 in class 4.6, 8.8 or 10.9. The Koyda guide shows the clearance hole (BS EN 1090-2 for structural steel, ISO 273 for general engineering), the minimum and maximum end, edge and pitch distances from BS EN 1993-1-8 Table 3.3, the stress area and minimum tensile load from BS EN ISO 898-1, and the maximum tightening torque and preload at the friction you pick, from the VDI 2230 table published by Bossard. Structural bolts are usually snug-tight; resin anchors follow the product's ETA.
Cite this: Koyda Ltd, “Bolt and Fixing Guide”, https://www.koyda.com/bolt-and-fixing-guide/, reviewed 10 October 2026.
Bolt guide
Guidance only. Torques are indicative maximums at the friction you pick, from a published VDI 2230 table. Structural bolts follow the engineer's design and BS EN 1090-2. Read the limits
Clearance hole
Max tightening torque
Bolt
End, edge and pitch distances (BS EN 1993-1-8, Table 3.3)
| Distance | Minimum | Maximum |
|---|
All sizes in this class and friction
| Size | As mm² | Hole (structural / ISO medium) | Max preload kN | Max torque Nm | Min edge 1.2d0 |
|---|
Use the tables and calculator offline
Install the Koyda app: section tables, weight calculator, CSV and PDF downloads, even without signal on site.
Resin anchors
Resin and chemical anchors: follow the product's ETA
Resin anchor performance depends on the product, the base material and the installation, so there is no general table to copy. Every number comes from the manufacturer's European Technical Assessment (ETA) for that product.
- Concrete: look for an ETA to EAD 330499 (bonded fasteners for use in concrete). It gives the characteristic resistances, the drill diameter, embedment depths, minimum edge distance and spacing, minimum member thickness, and cure times by temperature.
- Masonry: look for an ETA to EAD 330076 (metal injection anchors for use in masonry). Hollow brick and block need the mesh sleeve the ETA names.
- Design: anchors in concrete are designed to BS EN 1992-4. Selection, installation and site testing follow BS 8539, the UK code of practice for post-installed anchors.
- On site: drill, clean (blow, brush, blow as the ETA sets out), inject from the bottom, insert the rod, and leave it to cure for the full time before loading. Use the torque in the ETA, not a general table.
- Safety critical: balustrades, handrails, canopies and anything overhead need a designed fixing and, where BS 8539 calls for it, proof or allowable load tests on site.
Structural bolts
Bolted steelwork in practice
- Non-preloaded bolts: at least snug-tight to BS EN 1090-2 8.3, the parts pulled into firm contact. Snug-tight is what one person reaches with a normal-sized spanner and no extension arm. No torque value is specified.
- Preloaded bolts (slip-resistant joints): an EN 14399 bolt, nut and washer set, tightened by a method in BS EN 1090-2 with the k-class the supplier declares. Do not use the torques above.
- Holes: BS EN 1090-2 normal round holes (+1 mm for M12 and M14, +2 mm for M16 to M24, +3 mm from M27).
More: Bolt sizes, grades and holes · BS EN 1090 execution classes
Where the numbers come from
Sources
- Torque and preload: Bossard, "Preload and tightening torques" (01-2025), the VDI 2230 (2015) table for metric coarse threads: maximum values at 90% of yield, the same friction in the thread and under the head, ISO 273 medium holes.
- Stress area and minimum ultimate tensile load: BS EN ISO 898-1:2013, Table 4. Yield and tensile strengths fyb, fub: BS EN 1993-1-8 Table 3.1.
- Clearance holes: ISO 273 fine, medium and coarse series; BS EN 1090-2 normal round holes for structural bolts (M12 and up).
- End, edge and pitch distances: BS EN 1993-1-8 Table 3.3, minimums from d0, maximums from the thinner outer part t.
- Sizes: M3 to M33. M32 is not in these source tables; M33 is the next size they list.
Limits
Read before you tighten
- The torques are maximums with no safety margin. Tool scatter, a different finish or a lubricant changes the preload a lot.
- Not for preloaded (HSFG) structural bolts, stainless steel, fine threads, or bolts into tapped holes in soft metals.
- Maximum edge and pitch distances apply to steel exposed to the weather or other corrosion; weathering steel (EN 10025-5) has its own limits.
- No bolt resistances are given: the engineer designs the connection.
Guidance only
Guidance only. Torques are indicative maximum values from the VDI 2230 table published by Bossard: they assume 90% of the bolt's yield strength, the stated friction on the thread and under the head, ISO 273 medium holes and no safety margin. Friction varies with the finish, lubrication and condition, so use the bolt or fastener supplier's figures where you have them. Structural connections follow the engineer's design and BS EN 1090-2: non-preloaded bolts are snug-tight, preloaded bolts use an EN 14399 system and the method in BS EN 1090-2. This is not a substitute for a structural engineer.
Questions
Frequently asked questions
What torque should I use for an M12 8.8 bolt?
It depends on the friction. The VDI 2230 table published by Bossard gives a maximum of 73 Nm at a friction coefficient of 0.10, rising to 93 Nm at 0.14, for 90% of yield. These are maximum values with no margin. For structural steelwork the engineer's specification and BS EN 1090-2 apply: most bolts are only snug-tight.
Why does the friction coefficient matter so much?
Most of the tightening torque is used to overcome friction under the head and in the thread. With lower friction, the same torque gives much more preload, which can yield or break the bolt. Bossard's guidance is to use the lowest friction likely in practice when you are not sure. Their example: electro-zinc-plated parts range from about 0.14 to 0.24.
What does snug-tight mean?
BS EN 1090-2 (8.3) describes snug-tight as the tightness reached by one person with a normal-sized spanner and no extension arm, with the parts pulled into firm contact. It is the normal condition for non-preloaded structural bolts. No torque value is set.
How close to the edge can a bolt hole be?
BS EN 1993-1-8 Table 3.3 sets a minimum end and edge distance of 1.2 × the hole diameter (d0), a minimum pitch of 2.2 d0 along the force and 2.4 d0 across it. For an M20 bolt in a 22 mm hole, that is 26.4 mm to the edge and end. The bolt's bearing resistance is lower near the minimums, so engineers often use more.
What clearance hole should I drill?
For structural steelwork, BS EN 1090-2 sets the normal round hole: 1 mm over the bolt for M12 and M14, 2 mm for M16 to M24, and 3 mm for M27 and larger. For general engineering, ISO 273 gives fine, medium and coarse series (for M10: 10.5, 11 and 12 mm).
How do I choose a resin anchor?
From the manufacturer's European Technical Assessment (ETA) for that product and base material. The ETA gives the resistances, hole size, embedment, edge and spacing distances, cure times and installation steps. Follow it exactly, and get the fixing designed where it is safety critical.
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