Alumina thermocouple insulators and multi-bore tubes
Ceramic thermocouple insulators with one, two or four bores, in C799 alumina, OD 2–12 mm and cut to length. 15 sizes are usually in stock, including twin- and four-bore insulators from OD 2.5 to 8.5 mm with bores of 0.6 to 1.8 mm. Small orders ship in about 3 days.
- outer diameter
- 2–12 mm
- outer diameter
- bores
- 1, 2 or 4
- bores
- usually in stock
- 15 sizes
- usually in stock
- to ship
- ~3 days
- to ship
Insulators from our factory
See all 9 photos
Configurations
- Single bore
- Double bore
- Multi-bore
- Round
- Elliptical
- Capillary
Applications
- Thermocouple wire separation
- High-temperature electrical insulation
- High-frequency electrical insulation
Ordering
- Minimum order, non-standard parts
- 100 pcs
- Usually, per item made to your drawing or sample.
- Samples for approval
- 5–10 pcs
- Usually sent for you to approve before the order runs.
- Production lead time
- 25–30 days
- Usual production cycle for non-standard parts.
- Standard sizes from stock
- ~3–7 days
- Stock covers most standard sizes. Small orders ship in about 3 days, bulk orders in about 7 days.
Typical terms. Quantities and dates for your order are confirmed in its quotation.
Standard sizes
Size range
- OD
- 2–12 mm
- Length
- 10–4000 mm
Other sizes made to drawing; tolerances confirmed per quotation.
Usually in stock
Dimensions in mm
| OD | 1 boreBore Ø | 2 boresBore Ø | 4 boresBore Ø |
|---|---|---|---|
| 2.5 | 2.5 × 1.5 mm, 1 bore | 2.5 × 0.7 mm, 2 bores | 2.5 × 0.6 mm, 4 bores |
| 3 | 3 × 2 mm, 1 bore | — | — |
| 3.5 | — | 3.5 × 0.9 mm, 2 bores | 3.5 × 0.8 mm, 4 bores |
| 4.2 | — | 4.2 × 1.1 mm, 2 bores | 4.2 × 1.0 mm, 4 bores |
| 4.5 | — | 4.5 × 1.2 mm, 2 bores | 4.5 × 1.1 mm, 4 bores |
| 5.5 | — | 5.5 × 1.4 mm, 2 bores | 5.5 × 1.3 mm, 4 bores |
| 8.5 | — | 8.5 × 1.8 mm, 2 bores | 8.5 × 1.6 mm, 4 bores |
| 10 | 10 × 4 mm, 1 bore | — | — |
Standard sizes usually ship from stock in 3–7 days. Lengths are cut to order.
Bore Ø is the diameter of each bore. A dash means that layout is not listed for the OD. From our factory's standard-size list, September 2026.
Also made to order
Sizes from our earlier standard list. We make them to order; the lead time is confirmed in the quotation.
| OD | 1 boreBore Ø | 2 boresBore Ø | 4 boresBore Ø |
|---|---|---|---|
| 2 | 2 × 1 mm, 1 bore | 2 × 0.5 mm, 2 bores | 2 × 0.4 mm, 4 bores |
| 3 | — | 3 × 0.8 mm, 2 bores | 3 × 0.6 mm, 4 bores |
| 4 | 4 × 2.5 mm, 1 bore | 4 × 1 mm, 2 bores | 4 × 1 mm, 4 bores |
| 5 | 5 × 3 mm, 1 bore | 5 × 1.2 mm, 2 bores | 5 × 1.2 mm, 4 bores |
| 6 | 6 × 4 mm, 1 bore | 6 × 1.4 mm, 2 bores | 6 × 1.3 mm, 4 bores |
| 8 | 8 × 5 mm, 1 bore | 8 × 1.8 mm, 2 bores | 8 × 1.6 mm, 4 bores |
| 12 | 12 × 7 mm, 1 bore | — | — |
Flat twin-bore insulators
Flat, oval twin-bore insulators (flat cores) for photovoltaic and semiconductor use.
2.3 × 1.4 mm (width × thickness) usually in stock. 3 × 2, 3 × 1.8, 4 × 3 and 4.1 × 2.8 mm made to order, in lengths up to 4,000 mm.
Bore patterns we have made
- 1 bore
- 2 bores
- 3 bores
- 4 bores
- 4 bores, 2 + 2
- 5 bores
- 6 bores
- 7 bores
- 1 large + 2 small
End-face sketches, not to scale. Layouts from one to seven bores, including a large bore with two small ones. Smaller sizes have also been made: the smallest marked twin-bore insulator is about Ø1.5 mm OD.
Grade and material data
Alumina. Our standard grade is C799 alumina, 99.5% Al₂O₃, and we supply 95% white alumina where a drawing names C 610. The grade and bore layout are confirmed per SKU at quotation.
Full material data| Material class | Al₂O₃ % | Working temperature °C | Hardness, Mohs |
|---|---|---|---|
| High-alumina | >85 | 1300–1450 | 8 |
| Corundum | 99–99.5* | 1600–1800* | 8-9 |
* Stated per SKU: the grade and maximum temperature of each part are confirmed in its quotation.
Guides
Sizes, grades and tolerances in more detail.
- Buyer FAQ: minimum order, lead time, stock, samples, ISO 9001 and test reports What buyers ask before ordering: minimum order, lead time, which sizes are in stock, samples, the ISO 9001 certificate, lab reports and packing.
- Insulators for profile and spike thermocouples: flat and round twin-bore alumina, up to 4 m Flat and round twin-bore insulators for profile and spike thermocouples: sections, lengths to 4,000 mm, our sodium and silica analysis, and what to send.
- Kiln thermocouples: Type K or Type S, and the ceramic protection tube Type K or Type S in a pottery or industrial kiln, how long each lasts, what the ceramic protection tube does, and the alumina tubes and insulators we make for them.
- Alumina density, melting point and thermal properties by purity Density in g/cm³ and kg/m³, melting point, thermal conductivity and expansion for 96% and C799 alumina, with our forming-method data and a weight calculator.
- C799 alumina, C 610 and C 530: what the ceramic tube grades mean What the class numbers on a drawing mean, which one suits which thermocouple and atmosphere, and the old KER 710 and KER 610 names.
- Low-sodium alumina: Na₂O content, why it matters and how to specify it What low-sodium alumina means, the Na₂O, SiO₂, Fe₂O₃ and CaO in three years of lab analyses of our 99.5% alumina, why sodium matters for semiconductors and hot insulation, and what to put on the request.
- DIN 40680 tolerances for alumina tubes, and what buyers write on orders The OD, ID and length tolerances on this year's orders for protection tubes and insulators, set against the DIN 40680 general tolerances.
- Thermocouple insulator sizes: which bore for which wire diameter Compare wire diameters in mm and AWG with standard single-, twin- and four-bore insulators, then check minimum bore and maximum wire before ordering.
- Thermocouple types and temperature ranges, and the protection tube each one needs Thermocouple tolerance ranges, practical wire-size limits, and choosing insulation and protection tubes for the operating atmosphere.
- How to cut an alumina tube, and when to order it cut The diamond blade, speed, coolant and support that tool makers give for cutting fired alumina tube, and what a cut-to-length order from us looks like.
- Ceramic tubes and insulators for Type S, R and B thermocouples Which insulator and tube a platinum-rhodium thermocouple needs: the sources on silica and iron, stocked twin-bore sizes for 0.35 and 0.5 mm wire, tube fits and double tubes.
- High-temperature wire insulation: sleeving ratings, and ceramic insulators for heating wire Which insulation for which temperature, from PVC to ceramic fibre sleeving, then what heating wire needs from a ceramic: Kanthal’s rules, resistance when hot, bore sizes and forms.
- Thermocouple parts, from the measuring point to the head A labelled diagram and parts list for a straight industrial thermocouple, what each DIN EN 50446 model code means, and which ceramic parts to order for a rebuild.
- How alumina tubes are made: forming, sintering at 1,760 °C, and size limits Our process step by step: extrusion and slip casting with their largest sizes, the kiln temperatures for alumina and porcelain tubes, straightness, and what each step means for a drawing or order.
- Thermocouple insulator beads: beads or one-piece insulators, bead types and sizes When to thread beads and when to use a one-piece insulator, round, oval and fish-spine beads with their makers' ratings, and our alumina beads in every insulator size, cut to length.
Questions buyers ask
- Which thermocouple insulator sizes do you keep in stock?
- 15 single-, twin- and four-bore sizes from OD 2.5 to 10 mm are usually in stock, and another 18 sizes are made to order. Both tables are on this page, and lengths are cut to order.
- How long can an insulator be?
- Our insulator range is OD 2–12 mm and 10–4000 mm long, cut to the length you order. Flat twin-bore insulators of 2.3×1.4 mm (width × thickness) are usually in stock in lengths up to 2000 mm.
- Which bore size do I need for my wire?
- Compare the smallest finished bore with the largest wire diameter and leave a little clearance. Send the wire diameter and thermocouple type with your enquiry and we check the fit against our bore sizes.
- Do you sell insulator beads?
- Yes. We cut beads from long insulator tubes, so they come in the same sizes as our insulators. Give the bead length and quantity on your enquiry.
- What alumina grade are the insulators?
- Our standard grade is C799 alumina, 99.5% Al₂O₃. Where a drawing names C 610, we supply 95% white alumina instead.
- How fast do stock insulators ship?
- Stock sizes usually ship in about 3 days for a small order and about 7 days for a bulk order. Made-to-order sizes usually take 25–30 days to produce.
- Can we test samples first?
- Yes. We usually send 5–10 free samples, short pieces of the size you want, and you pay the courier.
What to send for a quote
- 01Outside diameter and length
- 02Number of bores, bore diameter and layout
- 03Round, elliptical or capillary section
- 04Wire diameter and thermocouple type
- 05Al₂O₃ grade, or your operating temperature
- 06Quantity
Next family:High-temperature alumina and corundum furnace tubes
Request a quote
Get a quotation for insulators & multi-bore.
Tell us the dimensions, grade and quantity. We confirm the grade, dimensions and tolerances in each quotation. Our yearly lab reports are available on request.