When a Bolt Outgrows the Hardware Aisle
Below M20, bolts are a commodity. Above it, the shelves thin out fast: an M30×2 in a 400 mm length, an M42 with a square head, a 2½" UNC stud for a fifty-year-old press — these aren't stock items anywhere. Distributors quote long waits and high minimums because someone upstream has to make the part anyway.
We are that someone, minus the middle step. EKINSUN turns large bolts directly from certified bar on CNC lathes — thread, head and shank machined to your drawing or measured from your broken original.
Machined or Forged? An Honest Answer
Big bolts come from two worlds, and the right one depends on your job:
| Hot-forged (a forge house) | Machined from bar (us) | |
|---|---|---|
| Best at | High-volume structural hardware — towers, bridges, steel erection | Singles to a few hundred; specials; replacements |
| Tooling | Heading dies — economical only at volume | None — geometry is a CNC program |
| Geometry | Standard heads and grades | Any head, shank step, shoulder, drilled feature, thread combination |
| Lead time at qty 1–50 | Often quoted in months, if at all | Days to a few weeks |
Need 5,000 standard A325 structural bolts? Go to a forge — genuinely. Need one M36 replacement or fifty M48 tie bolts with a machined shoulder? That job was designed for a lathe.
The Jobs That Land on Our Bench
"The M42 tie bolt on our press sheared. OEM says 14 weeks."
Send both halves — together they carry the full geometry. We measure thread, grip length and head, machine from 42CrMo4, and typically ship in a fraction of an OEM lead time. Order a spare in the same run; the second piece costs far less than the first.
"Crusher and mill anchor bolts in odd lengths — nobody stocks them."
Long anchor and foundation bolts to your exact length and thread projection, with square or heavy hex heads, bent J/L forms excepted — straight machined forms are our territory, delivered with matching nuts and thick washers.
"Big stainless bolts with an obsolete thread on a shaft coupling."
A4-80 and duplex machined to the original spec — including pre-metric and imperial threads (BSW, UNC 2½"+) that modern catalogs dropped decades ago. We gauge the old thread and match it, not approximate it.
Where the Catalogue Stops for a Bolt This Size
Above M20 the shelf thins out fast, and above M36 it mostly disappears outside a few stock lengths. But not every gap is ours to fill — two of the rows below send you somewhere else on purpose. EKINSUN LTD is a custom parts manufacturer, so the honest line first: on the stocked A325 structural sizes a distributor will always be cheaper, and we will tell you so in the quote. One pairing rule saves a failed inspection: heavy hex structural bolts to A325 take A563 DH or A194 2H nuts — the grades, dimensions and substitution rule live on the heavy hex nut dimensions page, and every hex pattern and spanner size sits on the family head — hex bolts & hex head bolt dimensions. Working on the nut side instead? The large hex nut dimension table, M56 to M160, gives across-flats, height, weight and the bar stock each size needs, and marks which pitches you can actually buy.
| What you need | Off the shelf? | What we actually do |
|---|---|---|
| M20×80 hex bolt, class 8.8, zinc plated | Yes, stocked | Buy it from a distributor. Nothing machined from bar will beat a stock price on a standard size. We will tell you so. |
| Certified A325 / F3125 structural bolts for a steel frame | Yes, and certified | Buy those too. Structural bolts carry a head marking tied to a certified production route; a bolt turned from bar cannot carry that marking, and no checking engineer should accept one. This is a hard limit, not a capacity issue. |
| The same M20 bolt, but 137 mm long because the stack says so | No | Length to the drawing, to the millimetre. An intermediate length costs the same to turn as a catalogue one. |
| M72 or M100 in a length nobody lists | No | Turned from bar — no heading die, so diameter is limited by bar stock and machine capacity, not by tooling cost. |
| Fine or left-hand pitch at a large diameter | Rare to none | Single-point turned to the pitch you specify, gauged to ISO 965 6g or the imperial class your drawing calls. |
| Heavy hex head, but with wrench flats cut down to clear a housing | No | Head milled to the across-flats you can actually get a spanner on, not to a table. |
| A bolt in aluminium 6061 or 7075 to save weight | Rare | Usually the wrong answer, and we will say so. At M20 and above an aluminium bolt carries a fraction of the clamp load of an 8.8 steel one. We machine it where the joint is genuinely light duty — guarding, jigs, instrument frames — and steer you to steel everywhere else. |
| Replacement for a bolt on a machine whose maker is gone | No | Reproduced from the worn original. Worn diameters are taken back to the original nominal, never to the measured worn value. |
Materials, Classes & Certificates
| Material | Class / grade | Typical use |
|---|---|---|
| Carbon steel C45 | ~8.8 equivalent | General machine bolts, base plates |
| Alloy 42CrMo4 (1.7225) | 10.9 / ASTM B7 equivalent | Press tie bolts, high-load joints — quenched & tempered |
| Stainless A2-70 (304) | 70 | General corrosion resistance |
| Stainless A4-80 (316L) | 80 | Marine, chemical, washdown |
| Duplex / super duplex | per spec | Offshore and aggressive media |
- EN 10204 3.1 material certificate traceable to bar heat, from series quantities — not on samples or single pieces
- Hardness and tensile testing for critical joints
- Thread gauging to ISO 965 6g (or the imperial class your drawing calls)
- Finishes: plain, black oxide, zinc, hot-dip galvanized via partner, passivated stainless
Matched sets: large or non-standard nuts and thick washers are machined in the same material and finish, so the whole joint arrives as one matched package — no hunting a second supplier for an M64 nut.
Frequently Asked Questions
A heavy hex bolt uses a larger across-flats dimension and a thicker head than a standard hex bolt of the same thread size, so the bearing face is wider and the head is better able to carry a high clamp load without digging into the joint. The thread itself is unchanged. Heavy hex is a head form, not a grade: it says nothing about strength class or certification on its own. We machine the heavy hex form in any diameter and material we can turn, including sizes and pitches that no standard covers.
Up to roughly M100 (4") diameter and past 1000 mm long, turned from solid bar. Above that, or for forged heads on structural volume, a forging house is the right supplier — and we'll say so.
Forging wins on cost at high volume in standard grades. Machining wins for 1–500 pieces, non-standard geometry, exact lengths, unusual materials, and replacements nobody stocks — no die, no tooling charge, no minimum.
Yes — EN 10204 3.1 certificates traceable to the bar heat, available on series quantities (not on single pieces), plus dimensional and hardness reports on request. Critical bolts are machined from certified 42CrMo4, class 8.8/10.9 steel, A4-80 or duplex bar.
Yes — a typical order. Send the broken bolt (both halves) or the dimensions; we confirm the drawing with you and machine the replacement, usually far inside the OEM lead time.
Yes — large hex, round or castellated nuts and thick washers in the same material and finish, delivered as a matched, certified set.
Get Large Bolts Quoted
Drawing, dimensions or the broken bolt. Engineers reply in 12h.
// Qty & price
1 pc
Sample price
Confirm fit before a run
10–50
Unit price drops
Setup cost shared
100+
Best price
All tiers quoted upfront
- →No distributor — you pay the maker directly
- →CAD saved after first order — reorder anytime at lower unit price