Better than electrical tape by far!
Used this on vehicles (starters) and trailer lights. Easy to use, looks like a professional fitting, and seems to hold tight.
Verified Buyer · Verified Purchase★ Verified
3:1 Dual Wall · 10ft Short Pack
3/8"
3:1 Heat Shrink
Fits6–8 AWG9.5mm
3/8 inch heat shrink tubing fits 6–8 AWG wire and is the correct size for sealing a crimped 16–14 AWG butt splice, whose barrel measures 7–8mm. ABYC E-11 Table XI rates 8 AWG at 40A and 6 AWG at 55A — alternator leads, fuse-holder tails, and shore power feeds. At 9.5mm expanded, the tube clears bare 6 and 8 AWG conductors and recovers to about 3.2mm. Here is the sizing rule most charts skip: choose the tube from the widest point it must pass over, then confirm the recovered diameter is smaller than the narrowest thing it must grip. 3/8 inch satisfies both conditions across an unusually wide range, which is why it is the most-ordered size in this line. The hot-melt liner flows at 120°C, filling the step between an oversized barrel and a thin conductor. UL 224, 600V, -55°C to +125°C.
★★★★★4.7 · 225 verified ratings across the Helixal range
42 in stock · Ships in 24h
Order up to 42 online · need more? Trade pricing
Size3/8" · 9.5mm
Click any size to navigate · 10 ft per roll
$7.6510 ft spool
→ Dispatched within 24 hours — delivered in 1–3 days→ 30-day money-back guarantee — 30 days to return it
Qty
1
Secured by Stripe · No account needed
→Ships USA & Canada
→ISO 9001
→Ships 24h
SKU: B0FJN2SZ3H · 3/8" (9.5mm) · 10 ft
Spec Sheet
3/8"
data sheet.
Full industrial dual-wall adhesive spec in a convenient 10ft pack. Same 600V rated, waterproof polyolefin construction as the large bulk rolls.
Imperial Size
3/8"
Expanded diameter
Metric Size
9.5mm
Nominal
Roll Length
10 ft
Per spool
Wire Gauge
6–8 AWG
Bare conductor
Shrink Ratio
3:1
Dual wall
Construction
Dual Wall
Adhesive inner liner
Inner Layer
Hot Melt Adhesive
Waterproof seal
Voltage Rating
600V AC
UL 224 — 600 V rms
Temp Rating
-55°C to +125°C
Continuous service
Shrink Temp
100°C (212°F)
Shrinking starts
Adhesive Flow
120°C (248°F)
Keep heating until it shows
Material
Polyolefin
Outer sleeve
Flammability
Self-extinguishing
UL 224 Recognized
Color
Black
Standard finish
Standards
UL 224 Recognized
UL file E361230 · RoHS
UV Resistance
Yes
Outdoor safe
Waterproof
Yes — adhesive seal
360° coverage
Sizing over a connector? The Wire Gauge row above is for bare conductor. Heat shrink must be sized to the widest point it passes over, so a crimped butt splice or lug barrel needs a larger tube than the wire alone — a 22–18 AWG splice barrel measures 5–6mm, a 16–14 AWG barrel 7–8mm, and a 12–10 AWG barrel 9–11mm. Measure the barrel, allow about 20% clearance, and confirm the recovered diameter is smaller than the narrowest thing the tube must grip. Use the size calculator.
What the
trade says.
Verified Buyers ★ · Full Range4.7★★★★★225 ratings · 84% 5-starCombined verified-buyer rating for every Helixal product — all ratios, all sizes — not this size alone.
Good quality and sealing heat shrink
Heat shrink works good. Makes a nice sealed wire connection. Better than pre-cut heat shrink — you can make whatever length you want.
R Davis · Verified Purchase★ Verified
Smart format for repair work
Great for keeping several sizes on hand without the bulk. Same quality as the large rolls — the adhesive seals perfectly every time.
Travis M. · Verified Purchase★ Verified
Customer Reviews
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Sizing & Application — 3/8 inch, 10ft pack
The most-ordered size in the range. Buy ten feet first and find out whether it fits.
3/8 inch (9.5mm) is the highest-turnover diameter we sell, because it satisfies two conditions at once: it clears a crimped 16–14 AWG splice barrel at 7–8mm on the way on, and it recovers to about 3.2mm, tight on bare 6–8 AWG behind it. ABYC E-11 Table XI rates 8 AWG at 40A and 6 AWG at 55A. Precisely because it is the size most people commit to in bulk, it is the one worth proving on ten feet first.
What a fit test tells you that a size chart cannot
A size chart maps a nominal gauge to a nominal tube. Your connector is not nominal. Crimp barrels vary between manufacturers by a millimetre or more, insulated splices vary more than bare ones, and a barrel that has been through a crimper is a slightly different shape from the one in the catalogue drawing.
Ten feet is enough to answer the question directly. Slide the tube over your actual connector cold and confirm it clears without dragging. Shrink one piece and confirm the recovered wall grips the conductor behind the barrel rather than tenting over it. Check that a bead of adhesive appears at both ends — that bead is the seal, and its absence means the liner did not flow.
Do that once and the bulk decision stops being a guess. If the fit is right, the 60ft roll is materially cheaper per foot and the correct next purchase. If it is not, you have spent the price of a pack rather than discovering the problem sixty feet in, which at this diameter is the most common expensive mistake in the range.
3/8 inch short pack at a glance
| Property | Figure | Why it matters |
|---|---|---|
| Expanded diameter | 9.5mm (3/8") | Clears the 7–8mm crimped 16–14 AWG splice barrel |
| Recovered diameter | ≈3.2mm | Grips bare 6–8 AWG conductor behind the barrel |
| Bare wire range | 6–8 AWG | 40A for 8 AWG, 55A for 6 AWG (ABYC E-11 Table XI) |
| Fit test | Clear cold, grip hot, bead at both ends | Three checks that settle the bulk decision |
| Pack yield | ≈20 splices at 6 in | A full job, not a sample |
| Bulk equivalent | 60 ft roll | The right next purchase once the fit is proven |
A joint with no adhesive bead at the ends usually has a void inside it. That is the single check worth making on the first piece you shrink.
When the test says use something else
01 · The tube drags over your barrel
Step to 1/2 inch. Forcing it stretches the tube cold, and a pre-stretched tube will not close down to its rated recovery.
02 · It shrinks fully and still moves
The conductor is thinner than the 3.2mm recovered wall. Drop to 5/16 inch so the tube actually closes onto it.
03 · You already know the fit
Then skip the pack. The 60ft roll costs appreciably less per foot and this is the size you will use most.
04 · Above 600V
Rated 600V rms. On a 1000 Vdc system the conductor itself must be rated and tubing seals rather than insulates — a repair pack does not change the voltage class.
Keep reading →3/8" 3:1 Dual Wall — 60ft bulk roll · Heat Shrink Butt Connectors · Heat Shrink Size Calculator
How it shrinks.
01
Measure & Select
Verify the expanded diameter is 20–30% larger than your wire or connector. The tubing must slide freely before heat is applied — if it drags, go one size up.
02
Cut & Thread
Cut to length and thread onto the wire or cable before making the splice or crimp. Overlap each terminal or connector end by at least 10mm for a proper seal.
03
Apply Heat
The tubing starts shrinking at 100°C, but the adhesive liner only flows at 120°C — so keep the heat gun moving past the point where it looks shrunk. Start at the center and work outward to push air toward the ends. Adhesive will appear at the tube ends — that is your visual seal indicator.
04
Inspect
The tubing should be tight and uniform with adhesive visible at both ends. No gaps, lifting, or cold spots. Pull-test the finished connection to confirm the adhesive bond.
Size ReferenceExpanded vs.
Expanded vs.
recovered.
Actual 3/8" tube at full expanded diameter (9.5mm) and after heat recovery. Use this as your fit reference before cutting.
Expanded: 9.5mm — slides over 6–8 AWG
Shrink ratio: 3:1 on full heat
Use it on.
01
Try Before You Buy Bulk
Order a 10ft pack to verify the size fits your connector before committing to a large roll. Test fit, shrink one piece, then buy the bulk roll with confidence.
02
Field Repair Kits
Keep a set of short rolls on the service van or boat. Enough for any repair job without hauling large rolls — one 10ft roll handles most splices.
03
Stock Multiple Sizes Cheap
For the same cost as one large roll, stock several different sizes in short packs. Covers more connector diameters for the same investment.
04
Marine & Outdoor Spot Repairs
Seals individual connections on boat wiring, outdoor electrical, and trailer harnesses. Same waterproof adhesive seal as the large rolls — just 10ft.
05
Low-Volume Production
Ideal for small-batch cable assembly and prototype builds where a full bulk roll would sit unused. Cost-effective for runs of fewer than 50 connections.
06
One-Off Automotive Builds
Custom automotive and motorcycle builds often need several sizes in small quantities. Short rolls let you match every connection without leftover material.
Size Guide
3/8" Questions.
Technical Guides
All Guides →From the Blog
Free Tool
Heat Shrink Size Calculator
Read Guide →Ratios2:1 vs 3:1 vs 4:1 Heat Shrink Ratio Guide
Read Guide →Complete GuideHeat Shrink Tubing: The Complete Guide
Read Guide →SizingSize Chart & Selection Guide
Read Guide →How-ToHeat Shrink for Battery Terminals
Read Guide →AutomotiveAutomotive Wire Protection Guide
Read Guide →Also available — 3/8" in other lines
All 13 sizes.
View line overview →3/32"2.4mm10 ft1/8"3.2mm10 ft3/16"4.8mm10 ft1/4"6.4mm10 ft5/16"8mm10 ft
Current3/8"9.5mm10 ft
1/2"12.7mm10 ft5/8"16mm10 ft3/4"19.1mm10 ft1"25.4mm10 ft1-1/4"31mm10 ft1-1/2"38mm10 ft2"50.8mm10 ftRecovered diameter is approx. 1/3 of the expanded size shown · All sizes ship to USA & Canada