What Is a Solderstick? Solder Seal Connectors Explained

Solderstick connectors are solder seal connectors: one of the quickest ways to make a sealed, soldered wire join without a soldering iron or a crimp tool. If you work on a 4x4, a caravan, a boat or a trailer, you have probably seen them: a short clear tube with a silver band in the middle and a coloured ring at each end. Heat it with a heat gun and you end up with a soldered, insulated and sealed splice.

This guide explains what these connectors are, how they are built, what happens inside the tube when you heat it, and where they are (and are not) the right choice. It is written for 12V and 24V work: automotive, marine, caravan, solar DC, low-voltage garden lighting and electronics.

If you already know what they are and just want to fit one, skip to our step-by-step fitting guide.

Quick answer: a Solderstick is a heat shrink tube with a ring of low-temperature solder in the centre and a sealing ring at each end.

• You strip two wires, place the bare ends inside the tube under the solder ring, and heat it with a heat gun.
• The solder melts and flows through the strands, the tube shrinks down, and the end rings melt to seal the wire insulation.
• The result is a soldered, insulated, sealed join in one step, with no crimp tool or soldering iron.
• They suit 12V and 24V wire from 0.25mm2 to 6.0mm2. They are not for mains wiring or for heavy battery cable.

What is a Solderstick?

A Solderstick is a self-contained wire splice, the type of connector also sold as a solder sleeve, solder splice or waterproof solder butt connector. Everything you need to join two wires is already inside the tube: the solder, the insulation and the seal. You supply the stripped wires and the heat.

Solder sleeves are not new. Heat-recoverable solder sleeves have been used in aerospace and defence wiring for decades, mainly for terminating cable shields and making small splices. The version sold for automotive and DIY work is the same idea scaled for everyday wire sizes and colour coded so you can pick the right size at a glance.

The main reason people use them is speed and consistency. A traditional soldered splice needs an iron, solder, flux, a separate piece of heat shrink and a steady hand. A crimped butt splice needs the right crimp tool and, if you want it sealed, a second layer of adhesive heat shrink. A Solderstick does the soldering, insulating and sealing in one heating step.

How Solderstick connectors are built

Every connector has three working parts. Understanding them makes it much easier to get a good join every time.

The clear heat shrink tube

The body of a Solderstick connector is clear polyolefin heat shrink tube. Polyolefin is the same family of material used for most general-purpose heat shrink: it shrinks when heated and becomes a tough insulating layer once it cools. Because the tube is clear, you can see the wires and the solder inside, which is the main way you check the join (more on that below).

The low-temperature solder ring

In the centre of the tube is a band of low-temperature solder, usually with flux built in. When the tube is heated, the solder melts, the flux helps it wet the copper, and the solder flows into and around the strands of both wires. When it cools, the two wires are joined electrically by the solder, the same way a hand-soldered splice is.

We do not publish a melting temperature for the solder ring. What matters in practice is that it is designed to melt at a temperature a normal heat gun reaches easily, without overheating the wire insulation if you work steadily.

The coloured sealing rings

At each end of the tube is a coloured ring of heat-activated adhesive. When the tube shrinks, these rings melt and grip the wire insulation, sealing the ends so moisture and dust cannot creep in along the wire. The colour also tells you the wire size the connector is made for: white, red, blue or yellow.

This is the part people often overlook. A connector that has been heated enough to melt the solder but not enough to flow the end rings is soldered, but it is not sealed.

How a Solderstick works when you heat it

Here is what happens, in order, when you heat one of these connectors over a pair of stripped wires.

1. The tube starts to shrink. Heat shrink starts to recover before the solder melts, so the tube closes down and holds the wires in position.
2. The sealing rings soften. The coloured rings at each end start to melt and flow against the insulation.
3. The solder ring melts. The silver band slumps, loses its shape and flows into the bare strands. You will see it change from a neat band into a shiny fill around the wires.
4. The tube finishes shrinking. The tube pulls tight over the soldered join and the sealed ends.
5. Everything cools and sets. The solder freezes, the adhesive sets and the join becomes solid. Do not move or bend it until it has cooled.

With a heat gun the whole process is quick. The full method, including stripping, joining the wires and heat gun technique, is in our step-by-step fitting guide.

What they are good for

They suit permanent, low-voltage splices where you want the join sealed and you do not need to unplug it later. Typical jobs include:

• 4x4 and car accessories: extending a light bar or spotlight loom, splicing in a reversing camera, repairing a chafed wire behind a bumper, adding a UHF radio or dash cam feed.
• Trailers and caravans: repairing trailer light wiring, joining a new tail light pigtail, fixing 12V lighting and pump wiring in a caravan.
• Boats: splicing nav light, bilge pump and sounder wiring where moisture is a constant problem.
• Solar DC and garden lighting: low-voltage garden light runs, small solar controller and lighting circuits.
• Electronics and hobby work: sensor wires, LED strips and other small-gauge wiring, using the white size.

In each case, the job is a splice between two wires of a similar size, out in an environment where water, dust or road grime would eventually get into an unsealed join.

Where they are not the right choice

Being honest about the limits is part of using them well. Do not use them for:

• Mains wiring. Solderstick connectors are for low-voltage work only. Never use them on 230/240V mains. In Australia, fixed mains wiring must be done by a licensed electrician.
• Battery cables and heavy cable. For battery cables and anything heavier than 6mm2, use crimped or soldered lugs, not splice connectors. The largest Solderstick connector (yellow) covers 4.0 to 6.0mm2.
• Joins you need to undo. This type of join is permanent. If a part gets removed for service, such as a light bar, a trailer plug or a fridge, put a proper plug in the circuit. Our guide to Deutsch connectors covers one popular option.
• Fixing undersized cable. A connector does not make a thin wire carry more current. Size the cable and the fuse for the load first. Our wire gauge guide for 12V and 4x4 wiring explains how.

There is also a judgement call on high-vibration runs, such as wiring that moves with the engine or hangs unsupported. Any soldered join makes the wire stiff right where the solder stops, so the wire either side needs support. Some people prefer a crimp with adhesive heat shrink for these runs. We compare the options in detail in Solderstick vs crimp vs solder.

Solderstick compared with other wire joins

Here is how they stack up against the other common ways of joining low-voltage wire.

The short version: they are the easiest way to get a soldered and sealed splice, but they are a splice, not a plug, and not a battery terminal.

Solderstick sizes and colours

The connectors are colour coded by wire size. The colour of the end rings tells you which wire the connector suits.

One thing catches a lot of people out in Australia: auto cable is often sold by its overall diameter rather than the copper size. For example, Narva's 4mm single core cable has a conductor cross-section of about 1.85mm2, so it takes a blue connector, not a yellow one. Always go by the conductor size in mm2. Our Solderstick sizes and colour chart covers how to choose, including joining two different sizes, and auto cable sizes in Australia explains the labelling.

How to tell a good Solderstick join from a bad one

The clear tube is the big advantage here: you can inspect the join without cutting it open. Workmanship standards for solder sleeves, such as NASA's, look for the same things you can check at home.

Signs of a good join

• The solder band has fully melted and lost its original shape, and has flowed smoothly into the strands of both wires.
• The bare copper of both wires sits under the solder, centred in the tube.
• The tube has shrunk tight along its whole length with no loose sections.
• The coloured end rings have melted and you can see a little adhesive at each end, gripping the insulation.
• No strands are poking through or sitting outside the tube.

Signs to redo it

• The solder band still looks like a neat ring sitting on top of the wires. It has not melted properly: apply more heat, evenly.
• The tube is cracked, split, charred or bubbled. That is usually too much heat in one spot, often from a lighter or a heat gun held too close.
• One wire end is sitting outside the solder zone, or a strand has pushed through the tube.
• The ends have not sealed, with gaps between the tube and the insulation.

If a join fails inspection, cut it out and fit a new connector. This type of connector cannot be reopened and remade.

Is Solderstick waterproof?

Solderstick connectors carry an IP67 rating, which means they are dust tight and withstand temporary immersion in water. The seal comes from the adhesive end rings bonding to the wire insulation, so it only holds if those rings have melted and flowed properly, and if the wire insulation itself is in good condition.

IP67 is a strong rating for a wire splice, but it is not a rating for permanent submersion. For more on what the numbers mean, read our IP ratings explainer and is Solderstick waterproof?

Which should you use?

• If you are splicing two 12V or 24V wires between 0.25mm2 and 6.0mm2 and want the join sealed, use a connector in the matching colour.
• If you are joining battery cable or anything over 6mm2, use a crimped or soldered lug with adhesive-lined heat shrink.
• If the part will be removed for service, such as a light bar, trailer or fridge, fit a plug and socket, then use heat-sealing splices on the permanent side of the loom if needed.
• If the wire runs somewhere that flexes or shakes constantly, use a soldered splice only where you can support the wire either side, or use a crimp with adhesive heat shrink.
• If the wiring is 230/240V mains, stop and call a licensed electrician.

Frequently asked questions

Does a Solderstick actually solder the wires?

Yes. The silver band in the centre is real solder with flux. When it melts it flows into the strands of both wires and forms a soldered joint, the same as hand soldering, just without the iron.

Do I need a heat gun for solder sleeves?

A heat gun is the recommended heat source because it heats the tube evenly from all sides. A lighter or torch can scorch the tube and leave soot, so treat it as a last resort for a roadside repair only.

Are solder seal connectors as good as crimping?

They are different, not simply better or worse. They are easier to get right without special tools and are sealed out of the box, while a quality crimp handles constant vibration and flex better. Our comparison guide covers when to use each.

Can you use solder seal connectors on car wiring?

Yes, for 12V and 24V circuits from 0.25mm2 to 6.0mm2, such as lights, accessories, sensors and trailer wiring. Disconnect the battery negative first, and keep them away from battery cables and anything heavier than 6mm2.

Can solder sleeves be used on 240V?

No. Solderstick connectors are for low-voltage work only. In Australia, fixed mains wiring must be done by a licensed electrician.

Can you reuse a Solderstick?

No. Once heated, the tube has shrunk and the solder has set. To change a join, cut it out, strip fresh wire and fit a new connector.

What do the colours on Solderstick connectors mean?

The colour shows the wire size: white for 0.25 to 0.34mm2, red for 0.5 to 1.0mm2, blue for 1.5 to 2.5mm2 and yellow for 4.0 to 6.0mm2. Match the colour to the conductor size of your wire.

What to use

Most people start with an assorted kit so they always have the right size on hand. All Solderstick kits include all four colours, and independent reviewers including Big Clive, Electronics N More, Ross Lukeman and Samcrac have tested them on video. Solderstick connectors are ISO 9001 and CE certified, and IP67 rated.

• 50PCS kit: 10 white, 22 red, 13 blue, 5 yellow. A good glovebox or toolbox kit.
• 100PCS kit: 25 white, 35 red, 30 blue, 10 yellow.
• 250PCS kit: 40 white, 100 red, 90 blue, 20 yellow. Suits a full accessory fit-out or a caravan rewire.
• 500PCS kit: 80 white, 200 red, 180 blue, 40 yellow. For workshops and auto electricians.
• Bulk 100 packs of a single colour, if you go through one size faster than the others.
• Adhesive-lined heat shrink for covering crimped lugs, bundling spliced wires and adding strain relief.

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