Every few weeks someone sends us two lines and nothing else: a diameter, a pitch, a length. M11×1.5×35 mm, M11×1.5×75 mm. They have already searched, already found that the thread is perfectly normal, and already discovered that the bolt is not. EKINSUN LTD is a custom parts manufacturer; this page sets out which of these diameters the standards define, which ones are on a shelf somewhere, and how the rest get cut from bar.
What the standards actually say about M7, M9, M11, M15 and M17
Two separate lists decide whether you can buy a bolt. ISO 261 is the thread list: diameters and pitches, nothing about heads. DIN 933, DIN 931 and ISO 4017 are the product lists: they take some of those threads and give them an across-flats, a head height, a thread length and a tolerance. A diameter that appears in the first list and not the second has a thread you can cut and gauge, and no bolt anyone stocks.
| Thread | ISO 261 pitches (mm) | In DIN 933 / ISO 4017? | Across-flats in use | Tap drill, coarse (mm) | Stress area As (mm²) | Major ø in inches |
|---|---|---|---|---|---|---|
| M7 | 1.0 · fine 0.75 | No | 11 mm (DIN 931/933) | 6.0 | 28.9 | 0.2756 in |
| M9 | 1.25 · fine 1.0, 0.75 | No | 13 mm (one listing) | 7.75 | 48.1 | 0.3543 in |
| M11 | 1.5 · fine 1.0, 0.75 | No | 17 mm (one listing) | 9.5 | 72.3 | 0.4331 in |
| M15 | — not in ISO 261 | No | none — you choose | 13.5 (for ×1.5) | 145.1 | 0.5906 in |
| M17 | — not in ISO 261 | No | none — you choose | 15.5 (for ×1.5) | 191.0 | 0.6693 in |
| M25 | 2.0 · fine 1.5, 1.0 | No | none — you choose | 23.0 | 420.0 | 0.9843 in |
| M28 | 2.0 · fine 1.5, 1.0 | No | none — you choose | 26.0 | 536.0 | 1.1024 in |
Pitches from the ISO 261 table; DIN 933 size list as published by distributors, checked September 2026 — it runs M1.6 to M64 in the preferred series plus M3.5, M14, M18, M22, M27, M33, M39, M45, M52 and M60, and contains none of the diameters above. Tap drill = major diameter − pitch. Stress area As = π/4 × ((d2+d3)/2)², the ISO formula — it returns 58.0 mm² for M10 and 84.3 mm² for M12, the published values, so the figures for these sizes are on the same basis. Multiply As by the proof stress of the class to get the load the bolt is good for. Across-flats: what stocked listings use where any exist; there is no standard value for these sizes.
| Thread | Where you meet it | What that means for the order |
|---|---|---|
| M7 | Motorcycle and small-engine work; brake and fuel fittings | The one size in this group you can still simply buy — check the length before asking for a quote. |
| M9 | Flywheel and torque-converter bolt territory | Sold as a rarity and in steel only, so stainless or a different length means machining. |
| M11 | Engine and brake work | Where M11 is stocked at all, its shelf neighbours are brake-line ends and banjo bolts rather than bolts in a range of lengths. |
| M15 | The bicycle thru-axle thread | Sold as complete axles in fixed lengths. Thread right, overall length or head wrong, is a turned part. |
| M17 | Drain-plug and sump-plug thread | Always a vehicle-specific part, so there is no generic bolt to order in this diameter. |
| M25 | Shaft ends, cable glands and equipment spigots | The thread is standard and the bolt never was; expect to nominate the head yourself. |
| M28 | Agricultural and heavy equipment shafts | As M25 — the diameter is in the thread tables and in none of the bolt tables. |
Why a standard thread ends up with no standard bolt
ISO 261 was written as a thread system, not a product range. It lists every diameter that makes geometric sense in three columns of preference and expects industry to build products on the first column. Industry obliged: M6, M8, M10, M12, M16, M20 became the bolts, the nuts, the washers, the drills, the spanners and the assembly lines. The in-between diameters stayed in the thread tables, where taps, dies, gauges and thread inserts are still made for them — which is why an M11 × 1.5 tap is a catalogue item and an M11 × 1.5 bolt is not.
That asymmetry is the whole problem, and it has a consequence worth knowing before you order anything: the parts that exist for these diameters are repair parts, not assembly parts. Taps, thread-repair inserts and drain plugs, yes. Bolts, nuts and washers, almost never. If your search keeps returning thread-repair kits, that is not the search failing; it is an accurate picture of what the market decided to make for M9 and M11.
“I need custom hex bolts. Please share specs and pricing. M11×1.5×35 mm, M11×1.5×75 mm.”
That enquiry arrived in September 2026 and is the shape of nearly all of them: the buyer knows the thread exactly, needs two lengths, and has run out of places to look. Neither length is stocked anywhere we could find.
What is on a shelf today — and what has to be cut
We checked the metric fastener specialists in September 2026 rather than assume. The result is narrower than most buyers expect and wider than some fear: M7 is genuinely available, M9 and M11 exist as single listings, and M15, M17, M25 and M28 have no hex bolt behind them at all.
| What you need | In the catalogue? | What we machine |
|---|---|---|
| M7 × 1 hex bolt, class 8.8, a common length | Yes — metric specialists list it to DIN 931/933, 11 mm across flats | Nothing. Buy it off the shelf — a one-off cannot come near that price and we will say so in the quote. |
| M11 × 1.5 hex bolt, 80 mm, class 10.9 | Yes — one length, one specialist, $32.73 a piece, listed as rare | Nothing, if 80 mm is your length. That is the cheapest M11 bolt in the world and it is still $32.73. |
| M11 × 1.5 in any other length — 35, 55, 75, 120 mm | No | Turned from bar to the exact length under head, full thread or partial with a plain shank to h9. |
| M9 × 1.25 or M11 × 1.5 in stainless, or in class 12.9 | No — the listings that exist are class 10.9 steel only | 304 / 1.4301, 316L / 1.4404, titanium or 42CrMo4 quenched and tempered to 12.9, any length. |
| A hex bolt in M15, M17, M25 or M28 | No — no product standard covers these diameters | Across-flats and head height are yours to choose; we cut the head to the spanner or pocket you have. |
| The matching nut, washer or stud | Rarely, and rarely in the same place as the bolt | Nut single-pointed as a pair with the bolt so the fit is gauged together; washers turned from the same bar. |
| Left-hand thread in any of these diameters | No | Same operation, opposite lead — no tooling charge and no minimum. |
| A drilled head, wire-lock hole or non-standard head height | No | The head is machined rather than forged, so across-flats, height and drilled features cost nothing extra. |
Measure the thread first — then decide between stock and custom
Most wrong bolts are bought with the right diameter. Diameter is easy to read with a caliper; pitch is what sends parts back, and on these in-between sizes the diameter itself is often misread, because a worn M11 measures 10.8 and gets written down as M10.
- Ten crests on a rule. Lay a steel rule along the thread, measure from one crest to the eleventh, divide by ten. 10 mm over ten means a 1 mm pitch, 12.5 mm means 1.25, 15 mm means 1.5, 20 mm means 2.
- A thread pitch gauge. The leaf gauge with metric blades: the blade that seats against the light with no gap is the pitch. It works inside a nut, which the rule does not.
- Measure the diameter over the crests, and round up. A used thread is always under nominal. 10.85 mm on a shank is an M11, not an M10 — check it against the pitch before deciding.
- Watch for inch threads. Pitch = 25.4 ÷ TPI, so 20 TPI is 1.27 mm and 14 TPI is 1.814 mm. If the ten-crest reading is not a round number, see the metric-to-imperial near-miss chart before ordering anything.
- Write down five things. Major diameter, pitch, length under the head, across-flats of the head, and the class or material stamped on it.
| You measured | What it is | Do this |
|---|---|---|
| ø7 shank, 10 mm over ten crests | M7 × 1 — the ISO 261 coarse pitch | Buy it. Metric specialists stock DIN 931/933 M7 in class 8.8 with an 11 mm head. |
| ø9 shank, 12.5 mm over ten crests | M9 × 1.25 — coarse | One specialist listing exists, class 10.9, 13 mm head, flagged rare. Check its length; if it is wrong, send us the five numbers. |
| ø11 shank, 15 mm over ten crests | M11 × 1.5 — coarse | 80 mm class 10.9 is the one shelf length. Anything else is machined. |
| ø15 or ø17 shank, 15 mm over ten crests | M15 × 1.5 or M17 × 1.5 — outside ISO 261 | No bolt standard covers it. Measure the across-flats you need as well and send both. |
| ø11 shank, 10 mm over ten crests | M11 × 1 — the fine pitch | Rarer still than the coarse. Say which one you have; the two will not interchange. |
| Ten crests reads 12.7, 14.5 or 18.1 mm | An inch thread — 20, 17.5 or 14 TPI | Check the near-miss chart. A 7/16-14 is only 0.11 mm fatter than an M11 and will cross-thread the hole. |
“M11 in inches” — the near-misses that start, then jam
These diameters sit close to inch sizes, which is why so many of them are searched as bolt size in inches or bolt to standard. The conversion is arithmetic, but the conclusion is almost always the same: close on diameter, wrong on pitch, and a thread that starts is more expensive than one that refuses.
| Thread | Major ø | Nearest inch size | Difference | What happens if you try it |
|---|---|---|---|---|
| M7 × 1 | 0.2756 in | 9/32 in (0.2812 in) | 0.0056 in bigger | 9/32 is not a bolt size in any inch series — there is nothing to confuse it with. |
| M9 × 1.25 | 0.3543 in | 3/8-16 UNC (0.3750 in) | 0.0207 in bigger | UNC pitch 1.588 mm against 1.25 mm. The bolt is too fat to start and the pitch is wrong as well. |
| M11 × 1.5 | 0.4331 in | 7/16-14 UNC (0.4375 in) | 0.0044 in bigger | Only 0.11 mm apart on diameter, so a 7/16 bolt feels like it belongs in an M11 hole. Its pitch is 1.814 mm against 1.5: it cross-threads within two turns. |
| M15 × 1.5 | 0.5906 in | 19/32 in (0.5938 in) | 0.0032 in bigger | Closer than any pair on this page, and again not a bolt size — the nearest real one is 5/8 at 0.625 in. |
| M17 × 1.5 | 0.6693 in | 11/16 in (0.6875 in) | 0.0182 in bigger | A 11/16 socket will not sit on an M17 head and an 11/16 thread will not enter an M17 hole. |
| M25 × 2 | 0.9843 in | 1-8 UNC (1.0000 in) | 0.0157 in bigger | UNC pitch 3.175 mm against 2 mm. Often mistaken because both are called “one inch” in conversation. |
If it is a head bolt, a flywheel bolt or a torque-converter bolt
A large share of enquiries for these diameters are engine fasteners, and they carry two conditions the rest of this page does not.
- Many are torque-to-yield. They are designed to be tightened past their yield point, so a used one is longer than it left the factory. Copying the length off the old bolt reproduces the stretch, not the design. Send the manual figure alongside the bolt, or the drawing if you have it.
- Grade matters more than shape. Tell us the class the manual calls for. We cut 10.9 and 12.9 from 42CrMo4 quenched and tempered, with the mill certificate to EN 10204 3.1, and will not substitute a lower class to make a price.
- Thread run-out and the underhead radius are part of the design on a stretched fastener, not cosmetic detail. They are cut to the drawing, and where there is no drawing we measure them off the original and put them on one before anything is machined. See thread undercut and relief groove for how that transition is specified.
- Where a genuine OEM part is still available, buy it. We will say so if we find one.
What we cut, and what you get to choose
Because the head is machined rather than forged, everything a catalogue fixes becomes a free variable here. There is no die to pay for and no minimum to reach.
| Feature | Range | Note |
|---|---|---|
| Diameter | M3 – M36, every diameter including M7, M9, M11, M15, M17, M25, M28 | Above M36 see large & oversize bolts, to M100. |
| Pitch | Coarse, fine, left-hand, and pitches no catalogue carries | Single-point cut — the pitch is a program value, not a tool you have to own. |
| Length under head | 6 – 400 mm, any increment | 47 mm costs the same as 50 mm. Two lengths of one thread cost the same as two of the same length. |
| Across-flats | Your number — or matched to the spanner you already have | For M9 and M11 the stocked listings use 13 and 17 mm; nothing obliges us to. |
| Head height and form | Standard hex, heavy hex, flanged, reduced height, drilled for lock wire | Laser marking of class or part number has no tooling cost, so it suits single pieces. |
| Material and class | 8.8, 10.9, 12.9 in steel and 42CrMo4; 304 / 1.4301, 316L / 1.4404; brass CW614N; titanium | Mill certificate to EN 10204 3.1 on request; see the bolt grade chart. |
| Quantity | From 1 piece | Most orders on this page are one to four bolts for one machine. |
One family, several pages — where your size lives
| Page | What it covers | Go there when |
|---|---|---|
| This page | M7, M9, M11, M15, M17, M25, M28 — diameters between the preferred sizes | The diameter is the problem. |
| Hex bolts | DIN 933 / 931 dimensions M2–M72 and custom hex bolts M3–M36 | Your diameter is a preferred size and the length or head is the problem. |
| Non-standard thread bolts | Left-hand, odd pitch, BSW and legacy threads | The pitch is the problem, not the diameter. |
| Fine pitch above M64 | M120×3, M100×3 and the pitches no nut catalogue stocks | The part is large and the pitch is fine. |
| Replacement bolts from a sample | Reproducing a discontinued or OEM bolt with no drawing | You have the old bolt and no numbers. |
| Banjo bolts | Hollow bolts for brake and fuel lines, M10 to M16 | The bolt has a cross-drilled fluid path. |
| Wrench size chart · Clearance hole chart | Across-flats and hole diameters for the preferred sizes | You need the numbers for a size the standards do cover. |
How to order
- The thread — designation if you have it (M11×1.5), or the diameter over the crests plus a ten-crest reading. A photo of the bolt next to a rule works.
- Length under the head, and whether the thread runs full length or stops short with a plain shank.
- The head — across-flats, height, or simply the spanner you have.
- Class or material, and the finish if it matters: plain, zinc, black oxide, passivated.
- Quantity — one piece is fine, and two different lengths of the same thread cost no more to set up than two of one.
Quote within 12 hours. The drawing is rebuilt from your photo, sketch or the old bolt and confirmed with you before anything is cut; a single machined piece ships 5 working days after you approve it.
Frequently asked questions
Yes. ISO 261 gives M11 a coarse pitch of 1.5 mm, exactly the way it gives M10 a 1.5 and M12 a 1.75. The thread is standard; what is missing is the bolt. DIN 933 and ISO 4017, the standards that turn a thread into a hex head bolt with a defined across-flats and head height, list M1.6 to M64 in the preferred series plus M3.5, M14, M18, M22, M27, M33, M39, M45, M52 and M60 - and M11 is in none of them. That is why a thread every tap and die house can supply has almost no bolts behind it.
From a metric fastener specialist, in one length. When we checked in September 2026 the only stocked M11 x 1.5 hex bolt we could find was 80 mm long, class 10.9, 17 mm across flats, at $32.73 a piece, and the seller's own listing describes M11 bolts as extremely rare and not commonly available for distribution. If 80 mm is your length, buy it off the shelf. If it is 35, 55, 75 or 120 mm, or you need stainless, the bolt has to be machined.
There is no standard answer, because no standard gives M11 a head. The specialist listings that do exist use 17 mm across flats - the same spanner as a DIN 933 M10 - and M9 listings use 13 mm, the same as an M8. When we machine one of these bolts the across-flats is a free variable, so tell us the spanner you have or the pocket the head must fit, and the head is cut to it.
Subtract the pitch from the diameter: 7.75 mm for M9 x 1.25, 9.5 mm for M11 x 1.5, 13.5 mm for M15 x 1.5, 6.0 mm for M7 x 1, 23.0 mm for M25 x 2 and 26.0 mm for M28 x 2. That gives roughly 75 percent thread engagement, which is what the standard drill tables target for the preferred sizes too.
No. 7/16 in is 0.4375 in against 0.4331 in for M11, so it is 0.11 mm fatter and feels like it belongs. Its pitch is 25.4 divided by 14, or 1.814 mm, against the 1.5 mm of M11 x 1.5. The flanks are 0.31 mm out of step after one turn: it starts, it tightens, and it strips the first threads in the casting. Diameter is the number people check; pitch is the number that decides.
Yes, and for these diameters you will usually need to. A nut, a washer and a bolt in M9, M11, M15 or M17 are rarely stocked in the same place, and often not at all. We single-point the nut with the bolt on the same machine so the fit is gauged as a pair, and turn the washer from the same bar if the seat matters.
We can machine it to a drawing or from the old bolt, but two things have to be settled first. Many engine fasteners are torque-to-yield: they are designed to be stretched past yield on tightening, which means the used original is longer than it started and must not be measured as if it were the drawing. And the grade matters more than the shape - tell us the class the manual calls for, 10.9 or 12.9, and we cut it in 42CrMo4 quenched and tempered with the mill certificate to EN 10204 3.1. Send the bolt and the manual figure, not just the bolt.
Because ISO 261 defines a thread system, not a product range. It lays out every diameter and pitch that is geometrically sensible, in three choice columns, and expects industry to standardise products on the first column. The bolt standards did exactly that. So M7, M9, M11, M25 and M28 stayed in the thread tables - taps, dies, gauges and thread inserts are all available for them - while the hex bolt was never drawn. M15 and M17 are one step further out: they are not in ISO 261 either, and exist only because a bicycle axle or a drain plug needed that diameter.
EKINSUN LTD is a custom parts manufacturer that turns hex bolts in any metric diameter from M3 to M36, including M7, M9, M11, M15, M17, M25 and M28, in any length from 6 to 400 mm, coarse or fine pitch, left-hand included. Class 8.8, 10.9 and 12.9 in steel, plus 304 / 1.4301, 316L / 1.4404, brass CW614N and titanium. One piece minimum, drawing rebuilt free from a photo or the old bolt, quote within 12 hours.
Send the diameter and the pitch
Thread designation or a ten-crest reading, length under the head, the across-flats you need, class or material, quantity. A photo of the old bolt beside a rule is enough. One piece minimum, quote within 12 hours.