European thermocouple makers order closed-end ceramic protection tubes in a short series of sizes. For high-purity alumina (class C 799) it is 10×6, 15×10, 24×18 mm, OD × ID. For mullite (C 610) it is 10×7, 15×11, 24×19 mm. Standard lengths run from 200 to 2030 mm. We keep 8 European sizes in stock, from 6×4 to 26×20 mm.
The European size series
The clearest public reference is Morgan Haldenwanger's 2026 price list, which sells these closed-end tubes “according to DIN 43 724”:
| Class | OD × ID (mm) | Wall (mm) |
|---|---|---|
| C 799 | 10×6 | 2 |
| C 799 | 15×10 | 2.5 |
| C 799 | 24×18 | 3 |
| C 610 | 10×7 | 1.5 |
| C 610 | 15×11 | 2 |
| C 610 | 24×19 | 2.5 |
| C 530 | 26×18 | 4 |
At the same OD, the C 610 tube has the bigger bore: 10×7 against 10×6, 15×11 against 15×10. So when a drawing just says “10 mm tube”, ask which grade the ID was taken from before you order.
DIN 43724 itself has been withdrawn. DIN Media points to DIN EN 50446, which covers complete thermocouple assemblies rather than bare tubes. The size series stayed in use: the Morgan list above still sells tubes by it.
Our standard sizes, and which ones are in stock
This is the factory's own standard list. The middle column only compares dimensions; it says nothing about the material.
| OD × ID (mm) | Same size as | Lengths we make (mm) | Stock |
|---|---|---|---|
| 6×4 | Not in that list | on request | In stock |
| 8×5 | Not in that list | on request | In stock |
| 10×6 | C 799 series | on request | In stock |
| 10×7 | C 610 series | 300–2000 | Made to order |
| 12×8 | Not in that list | 300–2000 | Made to order |
| 15×10 | C 799 series | on request | In stock |
| 15×11 | C 610 series | 300–2400 | In stock |
| 16×12 | Not in that list | 300–2500 | Made to order |
| 17×12 | Not in that list | on request | In stock |
| 20×15 | Not in that list | 500–2400 | Made to order |
| 24×18 | C 799 series | 500–2400 | In stock |
| 26×20 | Not in that list | 500–2400 | In stock |
Our 26×20 is not the 26×18 size that C 530 outer tubes come in, so check the bore before swapping one for the other. 6×4, 8×5 and 17×12 are not in the Morgan list either.
Matching dimensions don't make a tube C 799 or C 610. Those are material classes, explained in our guide to C 799, C 610 and C 530. We quote each tube by its Al₂O₃ content: corundum at 99, 99.5 or 99.7%, or high-alumina at more than 85%. Tell us the grade you need and the quotation confirms the grade of the tube we ship.
Lengths
We have made protection tubes from 6–40 mm OD and 300–2500 mm long. Stock currently includes Ø16, Ø20, Ø25 mm tubes 2500 mm long, which is longer than the 2030 mm top of the European list.
Tubes are cut to the length you order. This year's orders ran from 300 to 2030 mm, including the standard 530, 740, 1030, 1430 and 2030 mm lengths.
Tolerances
As-fired ceramic tubes are usually toleranced to DIN 40680. For extruded tubes up to 30 mm, the medium class applies: ±0.30 mm on a 10 mm diameter, ±0.40 mm on 15 mm, ±0.50 mm on 24 mm, and ±1% of length above 1000 mm.
On the orders we supplied this year, buyers wrote ±0.35 to ±0.7 mm on the OD of closed-end tubes from 6 to 20 mm, and ±1 mm on length. The full table is in alumina tube tolerances.
What to send for a quotation
- OD × ID × length, and whether one end is closed.
- The Al₂O₃ grade, or your temperature, atmosphere and thermocouple type.
- Tolerances if you need them tighter than the ones above, and any insert that has to reach the bottom of the tube.
- Quantity and how often you reorder.
Standard sizes usually ship from stock: in about 3 days for small orders and about 7 days for bulk. Other sizes are made to drawing, usually in 25–30 days, from 100 pieces. See the protection tube page for grades and photos, or request a quote.
Sources
- Morgan Haldenwanger price list, valid from 1 January 2026: standard sizes and DIN 40680 tolerance table
- DIN Media: DIN 43724, withdrawn (DIN EN 50446 recommended)
- Our own figures: the factory's standard-size list, 2026 orders and test report, as recorded in our product catalog.