An M10 × 60 bolt is 10 mm across the thread and 60 mm long. Neither number says where the thread begins — and on a partly threaded bolt that third number decides whether the joint closes up at all.
A partly threaded bolt has a plain shank under the head and a threaded length at the free end. The division is fixed by the standard's thread-length column, not by the overall length, and nothing on the label or the head marking tells you where it falls. Everything below follows from that one gap.
The thread length is 2d + 6
| Size | Thread length b (mm) | 2d + 6 | Shortest ISO 4014 length (mm) | Shank there (mm) |
|---|---|---|---|---|
| M4 | 14 | 14 | 20 | 6 |
| M5 | 16 | 16 | 20 | 4 |
| M6 | 18 | 18 | 20 | 2 |
| M8 | 22 | 22 | 25 | 3 |
| M10 | 26 | 26 | 25 | 0 |
| M12 | 30 | 30 | 30 | 0 |
| M14 | 34 | 34 | 35 | 1 |
| M16 | 38 | 38 | 35 | 0 |
| M18 | 42 | 42 | 40 | 0 |
| M20 | 46 | 46 | 40 | 0 |
| M22 | 50 | 50 | 50 | 0 |
| M24 | 54 | 54 | 50 | 0 |
The second and third columns agree on every row. That is worth stating plainly, because it is not a coincidence to be assumed: it is what this table says, size by size, and it is why the ISO 4014 page can print a thread length for every size without a note qualifying it.
The offset is not a figure chosen for this article either. It is whatever the data holds: b minus 2d comes out to the same number on all 12 sizes, and the article prints that number rather than a remembered one. If the table ever stops agreeing with itself, this page stops building instead of printing a sentence that has gone false.
Some of these bolts are fully threaded
Read the shortest length against the thread length in the second column. On 5 of the 12 sizes the shortest length in the table leaves a shank behind, and even there it is a stub: M4 keeps 6 mm of it, M14 keeps 1 mm. A millimetre of plain shank is not a design feature — it is where the length series and the thread length happen to land.
On the other 7 the shortest length is at or below the thread length: M20 carries a thread length of 46 mm and starts at 40 mm.
A thread longer than the bolt cannot exist on a real part. What the row is telling you is that the thread runs from the free end up to `min(b, L)`, and the shank is whatever is left — which on a short enough bolt is nothing at all. Those first sizes are fully threaded in everything but name.
That is also why the fully threaded form, ISO 4017, starts earlier than this one: the same M4 begins at 10 mm there and 20 mm here. Below its own thread length a partly threaded bolt has no thread left to divide, so the shorter lengths are made fully threaded instead of being listed twice.
The shank is not slack in the part
M20 × 100 carries 54 mm of plain shank, 54 percent of the bolt's length. It is not a manufacturing allowance that could be trimmed away; it is the section between the head and the start of the thread, and it is the section the joint occupies.
Which sets a floor on the joint. If the material being clamped is thinner than that shank, the thread never reaches the outer face, and the nut has nothing to sit on.
The nut cannot pass the shank
| Size | Shank diameter (mm) | Nut thread minor (mm) | Overlap (mm) |
|---|---|---|---|
| M4 | 4 | 3.24 | 0.76 |
| M5 | 5 | 4.13 | 0.87 |
| M6 | 6 | 4.92 | 1.08 |
| M8 | 8 | 6.65 | 1.35 |
| M10 | 10 | 8.38 | 1.62 |
| M12 | 12 | 10.11 | 1.89 |
| M14 | 14 | 11.83 | 2.17 |
| M16 | 16 | 13.83 | 2.17 |
| M18 | 18 | 15.29 | 2.71 |
| M20 | 20 | 17.29 | 2.71 |
| M22 | 22 | 19.29 | 2.71 |
| M24 | 24 | 20.75 | 3.25 |
The shank is turned to the nominal diameter. The nut's internal thread is cut down to the minor diameter, 8.38 mm on M10, so the nut is 1.62 mm too small to pass over the shank. It is not a loose fit and it is not a stripped thread: the nut reaches the end of the thread and stops, and there is no more thread to travel on.
That is why this failure looks like a bolt that will not draw up rather than a joint that slips. Nothing is damaged, and no amount of torque closes the gap — the parts are the wrong pair.
Set the joint first, then the length
Two limits, and they pull in opposite directions:
- The shank must fit inside the joint. Shank = L − (2d + 6), so L ≤ t + 2d + 6, where t is the clamped thickness including washers.
- The bolt must reach past it. L ≥ t + m, with m the nut height from ISO 4032.
The room between those two limits is (2d + 6) − m, and that width does not depend on t at all. On M10 it is 17.6 mm: a thick joint and a thin one give exactly the same latitude in length, just at different absolute sizes. A partly threaded bolt is not "flexible within a range that grows with the joint" — the range is a constant set by the diameter.
| Size | Joint thickness (mm) | Longest ISO 4014 length (mm) | Shank (mm) | Past the nut (mm) |
|---|---|---|---|---|
| M4 | 10 | 20 | 6 | 6.8 |
| M4 | 15 | 25 | 11 | 6.8 |
| M4 | 25 | 35 | 21 | 6.8 |
| M4 | 40 | 50 | 36 | 6.8 |
| M6 | 10 | 25 | 7 | 9.8 |
| M6 | 15 | 30 | 12 | 9.8 |
| M6 | 25 | 40 | 22 | 9.8 |
| M6 | 40 | 50 | 32 | 4.8 |
| M10 | 10 | 35 | 9 | 16.6 |
| M10 | 15 | 40 | 14 | 16.6 |
| M10 | 25 | 50 | 24 | 16.6 |
| M10 | 40 | 60 | 34 | 11.6 |
| M16 | 10 | 40 | 2 | 15.2 |
| M16 | 15 | 50 | 12 | 20.2 |
| M16 | 25 | 60 | 22 | 20.2 |
| M16 | 40 | 70 | 32 | 15.2 |
| M24 | 10 | 60 | 6 | 28.5 |
| M24 | 15 | 60 | 6 | 23.5 |
| M24 | 25 | 70 | 16 | 23.5 |
| M24 | 40 | 80 | 26 | 18.5 |
Read the rows downward and the constraint is plain: the thinner the joint, the shorter the longest usable bolt. On a 10 mm joint no size in the table goes past 60 mm, because every longer one brings a shank that will not fit inside the material.
Long bolts are for thick joints
The constraint runs the other way at the top end too. The longest M24 length here is 200 mm, with 146 mm of shank: it will not close on anything thinner. And M24 in ISO 4017 stops at 120 mm, so every length above that exists only in the partly threaded form.
Put those two together and "long bolt, thin plate" has no answer in either product form. It is not a stock problem and not a supplier problem; there is no such part to order.
Where this stops
- Above 125 mm of length. The thread length here comes from a column keyed to lengths up to 125 mm. Longer bolts are in the standards, but their thread lengths are not in this database, so this page does not extend the rule upward.
- Preload, torque and strength. None of them are in this database, and the joint above is geometry only. Whether the bolt is strong enough is a separate question, covered for grade selection in how to choose a property class.
- Thread protruding past the nut. The lower limit above stops when the nut is just fully engaged. A real joint usually wants a few threads showing beyond it; that allowance is a shop convention, it is not in this database, and it is not included in any figure here.
- Washer thickness. The ISO 7089 washer table carries the thickness to add to the plate, and it is not counted in the examples above.
Choosing a length
- Measure the clamped thickness, and add the washer if there is one.
- Work out the ceiling: L ≤ t + 2d + 6. That is the longest partly threaded bolt that will close.
- Take the longest standard length at or below that ceiling — it leaves the most thread past the joint.
- Check it also reaches t + m, then add whatever thread you want showing past the nut.
- If the ceiling falls below the floor, the joint is thinner than the shank of any bolt long enough to reach through it. Go to the fully threaded ISO 4017 if a length exists, or step down a diameter.
The ISO 4014 page prints the thread length and the length range for every size, the ISO 4017 page prints the fully threaded range to compare against, and the fastener index lists what this database holds by diameter and length.