25 × 18 mm alumina thermocouple protection tube
OD 25 mm · ID 18 mm · wall 3.5 mm
- Standard size · usually in stock
An alumina sheath that shields the thermocouple wires and their insulator from the furnace atmosphere. We make it closed at one end or open at both, and cut it to the length you order.
Specifications
Nominal dimensions from our factory's standard-size list, September 2026.
| Outside diameter (OD) | 25 mm |
|---|---|
| Inside diameter (ID) | 18 mm |
| Wall thickness | 3.5 mmcomputed: (OD − ID) ÷ 2 |
| Length | Standard 300 / 450 / 600 / 1000 mm; other lengths cut to order |
| Ends | One-end closed · Open-ended |
| Availability | Usually ships from stock in 3–7 days |
| Material and grade | High-alumina (>85% Al₂O₃), corundum and mullite. Grades: 99.5% Al₂O₃ (C799-class) as standard, plus 99.7%, 99% and 95%, all available. Purity and maximum temperature are confirmed per SKU. |
Our insulators that fit inside
Insulators from our standard list whose OD is at least 1 mm smaller than this tube's 18 mm ID.
1 bore
How we worked it out: insulator OD + 1 mm ≤ tube ID, on nominal sizes, which leaves room for the tolerances of both parts. Check the fit against your own drawing.
Tolerances on our 2026 orders
No order tolerance is on record for this size yet. We state the tolerance in the quotation.
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.
Nearby sizes
Request a quote
Get a quotation for the 25 × 18 mm protection tube.
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.