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The correct cold shrink tube size comes from three matches. The expanded inner diameter must fit the largest part of the connector or cable. The recovered diameter must grip the smallest part. Length must cover the full joint with overlap. Expanded means the factory-stretched opening before the core is pulled. Recovered means the final opening after shrinkage. These two numbers decide how to choose cold shrink tubing that slides on easily and seals tight.
! Key Takeaways
- [✓] Measure the largest part of the connector or cable. Choose a tube with an expanded inner diameter that is 20%–50% larger, and at least 5mm larger, so it slides on easily.
- [✓] Check the smallest part of the cable. The tube’s recovered inner diameter must be smaller than that part to grip and seal tightly.
- [✓] Measure the full joint and add 20–50mm of overlap on each side. Make sure the tube is long enough to cover the joint and overlap after it shrinks.
Cold Shrink Tubing Sizing: Inner Diameter Selection
Cold shrink tubing sizing starts with two diameter checks. One check covers the slide-on step. The other covers the sealing step. Both numbers come from the same source: the cable/connector’s outer diameter at its widest and narrowest points.
Matching the Expanded Inner Diameter
The expanded inner diameter must clear the largest part of the connector or cable. A practical rule sets the expanded ID 20%–50% larger than that largest part, and at least 5mm larger. This margin lets the tube slide on without forcing. Forcing stretches the core and can damage the sleeve before installation.
Measure the widest point first. On an RF connector, that point is often the coupling nut or the backshell, not the cable jacket. Compare that measurement against the expanded ID printed on the datasheet. A tube that barely clears the nut will bind during the pull.
Matching the Recovered Inner Diameter
The recovered inner diameter must be smaller than the smallest part of the cable. This is the grip point. The tube presses down on the jacket and seals the joint. Some silicone cold shrink tubing for RF applications reaches shrink ratios as high as 4.5:1, according to Gamma Electronics. That high ratio lets the tubing fit over the connection first and still shrink tightly enough for a watertight seal once the core is removed.
Use this cold shrink inner diameter guide as a starting reference:
| Common RF cable size | Suggested expanded ID | Suggested recovered ID |
|---|---|---|
| 1/4 in. corrugated | 10–14mm | below 6mm |
| 3/8 in. corrugated | 14–18mm | below 9mm |
| 1/2 in. corrugated | 18–24mm | below 12mm |
The Telsto TEL-CST-32-9 shows the rule in practice. This silicone rubber cold shrink tube fits cables from 13.0–25.4mm. Its open-ended core design needs no tools or heat. The expanded ID clears the connector, and the recovered ID grips the jacket after the core pulls free.
How to Choose Cold Shrink Tubing Length
Length is the second half of the cold shrink tube size decision. A tube with the right diameter but the wrong length leaves part of the joint exposed. This length selection guide covers measurement, overlap, and worked examples for common RF joints.
Measuring the Joint and Adding Overlap
Measure the full joint first. Start at the connector face and end at the cable jacket where the exposed section stops. This span includes the connector body and any exposed cable section. Add 20–50mm of overlap on each side. Overlap lets the tube extend onto clean jacket beyond the joint.
When covering an RF connector joint, choose a cold shrink tube long enough to extend at least 1 inch (≈25 mm) beyond the connector onto the cable jacket on each side, unless the tube manufacturer specifies a different overlap requirement.
RF Connector and Jumper Cable Examples
| Size | As Supplied ID (mm) | As Supplied Length (mm) | After Recovery ID (mm) | After Recovery Length (mm) | Fit Range OD (mm) |
|---|---|---|---|---|---|
| Φ25/5.5-90 | 25±2 | 90±10 | 5.5±1.0 | 110±5 | 7.4–20 |
| Φ30/9-100 | 30±2 | 100±10 | 8.5±1.0 | 120±5 | 10–25 |
| Φ40/10-100 | 40±2 | 100±10 | 10.0±1.0 | 125±5 | 12.7–35 |
Outdoor RF connectors and jumper cables need UV-resistant cold shrink tubing. Sun exposure degrades standard materials over time. Silicone rubber and EPDM cold shrink resist UV aging and embrittlement. Check IP68 sealing as a fit check for harsh environments. An IP68 rating confirms the tube keeps water out under immersion, which matters for feeder cable waterproofing and weatherproofing for RF connectors.
Confirm the cold shrink tube size in three steps:
- Measure the largest part for the expanded inner diameter.
- Confirm the smallest part for the recovered diameter.
- Measure the joint plus overlap for length.
A correct fit slides on easily, shrinks tight, and seals the connection. Share your cable and connector specs with our support team to confirm the right cold shrink tubing.
FAQ
How do I measure the largest part of an RF connector?
Measure the coupling nut or backshell, not the cable jacket. Compare that value against the expanded inner diameter on the datasheet.
Does cold shrink tubing need heat or tools?
No. The tube arrives factory-expanded on a removable core. Pull the core, and the sleeve shrinks uniformly by hand.
What shrink ratio works for RF connectors?
Silicone cold shrink tubing for RF applications can reach shrink ratios as high as 4.5:1, according to Gamma Electronics. Confirm the recovered inner diameter grips the smallest part of the cable.
Post time: Oct-28-2026
