Light series, L (DIN 2353 / ISO 8434-1)
The medium pressure series. Larger tube on a given thread, thinner wall, lower rating.
60 degree flanksParallel24 degree cone (DIN)
Confusion pair
Metric L series vs S series (DIN 2353)
Seven threads carry one tube size in the light series and a different one in the heavy series. The thread tells you nothing about which fitting you are holding.
Heavy series, S (DIN 2353 / ISO 8434-1)
The high pressure series. Smaller tube on the same thread, heavier body, higher rating.
60 degree flanksParallel24 degree cone (DIN)
The three answers
What actually happens if you put them together
What interchanges
- Nothing across the series. The nut and body of one series will not correctly retain the cutting ring and tube of the other, even where the thread is identical.
What threads together and will still leak or fail
This is a safety statement, so it is only made where it is sourced. Each item below either cites a published statement that the two are not interchangeable, or rests on the figures on the size pages showing an identical thread with a different seat.
- M14, M16, M18, M22, M30, M36 and M52 each appear in BOTH series, carrying different tube diameters - M18 x 1.5 is 12 mm tube in the light series and 10 mm tube in the heavy series, and so on down the list. All four identification sources give the same map. A light-series nut will run onto a heavy-series body, and the cutting ring is bored for one tube diameter only: on the wrong one it does not bite properly, and the joint blows the tube out under pressure. The pressure ratings are far apart too - the light series is rated in the low hundreds of bar where the heavy series runs to 630.
What will not fit at all
- The tube itself. Even when the thread runs together, the tube diameter the fitting is bored for is a different number in each series, so the tube will either not enter or will sit with a gap the ring cannot close.
The check that settles it
Measure the TUBE, not the thread. The tube outside diameter and the thread together identify the fitting; the thread alone does not. Heavy series bodies are also visibly thicker across the hex flats for the same thread, and most makers stamp the series letter on the nut.
Size by size
Where the threads match, and where they do not
7 of the 13 sizes below run the same thread count within half a millimetre on diameter. Those are the rows that will screw together. Built from the published dimensions at page-build time, not from a hand-kept list.
| Size | Light series, L | Heavy series, S | Will they assemble? |
|---|---|---|---|
| M12 x 1.5 | M12 x 1.5 · 6 mm tube, light series | No such size | Only one family has this size |
| M14 x 1.5 | M14 x 1.5 · 8 mm tube, light series | M14 x 1.5 · 6 mm tube, heavy series | Yes, and it is the wrong joint |
| M16 x 1.5 | M16 x 1.5 · 10 mm tube, light series | M16 x 1.5 · 8 mm tube, heavy series | Yes, and it is the wrong joint |
| M18 x 1.5 | M18 x 1.5 · 12 mm tube, light series | M18 x 1.5 · 10 mm tube, heavy series | Yes, and it is the wrong joint |
| M22 x 1.5 | M22 x 1.5 · 15 mm tube, light series | M22 x 1.5 · 14 mm tube, heavy series | Yes, and it is the wrong joint |
| M26 x 1.5 | M26 x 1.5 · 18 mm tube, light series | No such size | Only one family has this size |
| M30 x 2.0 | M30 x 2.0 · 22 mm tube, light series | M30 x 2.0 · 20 mm tube, heavy series | Yes, and it is the wrong joint |
| M36 x 2.0 | M36 x 2.0 · 28 mm tube, light series | M36 x 2.0 · 25 mm tube, heavy series | Yes, and it is the wrong joint |
| M45 x 2.0 | M45 x 2.0 · 35 mm tube, light series | No such size | Only one family has this size |
| M52 x 2.0 | M52 x 2.0 · 42 mm tube, light series | M52 x 2.0 · 38 mm tube, heavy series | Yes, and it is the wrong joint |
| M20 x 1.5 | No such size | M20 x 1.5 · 12 mm tube, heavy series | Only one family has this size |
| M24 x 1.5 | No such size | M24 x 1.5 · 16 mm tube, heavy series | Only one family has this size |
| M42 x 2.0 | No such size | M42 x 2.0 · 30 mm tube, heavy series | Only one family has this size |
Detail
Everything each family carries
| Property | Light series, L | Heavy series, S |
|---|---|---|
| Flank angle | 60 degrees | 60 degrees |
| Parallel or tapered | Parallel | Parallel |
| Seat | 24 degree cone (DIN) | 24 degree cone (DIN) |
| Where it seals | The 24 degree cone against a cutting ring bitten into the tube, or against a soft seal captured in the cone on the sealing-cone version. | The 24 degree cone against a cutting ring bitten into the tube, or against a soft seal captured in the cone on the sealing-cone version. |
| Defined by | ISO 8434-1, DIN 2353 | ISO 8434-1, DIN 2353 |
| Sized by | Sized by tube outside diameter in millimetres AND by series: the same thread can carry two different tube sizes depending on whether it is light or heavy series. | Sized by tube outside diameter in millimetres AND by series: the same thread can carry two different tube sizes depending on whether it is light or heavy series. |
| Series | Light (L), medium pressure | Heavy (S), high pressure |
Answers
Common questions
Will a Light series, L screw into a Heavy series, S?
M14, M16, M18, M22, M30, M36 and M52 each appear in BOTH series, carrying different tube diameters - M18 x 1.5 is 12 mm tube in the light series and 10 mm tube in the heavy series, and so on down the list. All four identification sources give the same map. A light-series nut will run onto a heavy-series body, and the cutting ring is bored for one tube diameter only: on the wrong one it does not bite properly, and the joint blows the tube out under pressure. The pressure ratings are far apart too - the light series is rated in the low hundreds of bar where the heavy series runs to 630.
Are DIN 2353 light (L) and heavy (S) series interchangeable?
Nothing across the series. The nut and body of one series will not correctly retain the cutting ring and tube of the other, even where the thread is identical.
How do I tell them apart?
Measure the TUBE, not the thread. The tube outside diameter and the thread together identify the fitting; the thread alone does not. Heavy series bodies are also visibly thicker across the hex flats for the same thread, and most makers stamp the series letter on the nut.
More pairs
Other fittings people mix up
Where these figures come from
Every value on this page was checked against 5 independent published sources:
- Hydraulic coupling identification chart E2/50101 - Gates, Gates Europe, 2004 (manufacturer, read 2026-08-27)
- Fluid Ports and Connectors Identification Guide - McGill Hose & Coupling, SAE J512, J514, J1453, J1926-1, ISO 228, ISO 7, DIN 2353, JIS (distributor, read 2026-08-27)
- How to identify 24 degree tube fittings, component compatibility chart - Adaptall, DIN 2353, ISO 8434-1 (manufacturer, read 2026-08-27)
- Thread identification: BSP, JIC, ORFS and metric tables - Apex Fluid Power, ISO 12151-2, ISO 8434-1 (distributor, read 2026-08-27)
- High pressure pipe connectors: DIN 2353 working pressure table - Tubes International, DIN 2353, PN-ISO 8434-1 (distributor, read 2026-08-27)
Sources disagree: DIN 2353 heavy series, 30 mm tube, working pressure.
- 400 bar (adaptall-24)
- 250 bar as the ISO 8434-1 cutting-ring figure, 250 to 315 bar across producers (tubes-int)
The 400 bar figure sits outside the producer range the other source publishes for the same size band, which is the only place in the metric table where that happens. Both figures are printed on the size page. Assume the lower one unless the fitting's own catalogue says otherwise.