Solderstick Sizes: Colour Chart and Which Wire Each Fits

Solderstick sizes are marked by colour, as with most solder seal connectors, and picking the right one is the easiest way to get a strong, sealed join. Use one that is too big and the ends will not seal around the wire. Use one that is too small and the wires will not fit, or the solder will not reach every strand.

This guide gives you the full colour chart in AWG and mm2, explains how to work out what size your wire actually is (which is not always what the packet says), and covers the awkward cases: two different wire sizes, three wires in one join and wire that falls between sizes.

New to these connectors? Start with what a Solderstick is and how it works.

Quick answer: Solderstick connectors come in four colour-coded sizes:

• White: AWG 26-24, 0.25-0.34mm2
• Red: AWG 22-18, 0.5-1.0mm2
• Blue: AWG 16-14, 1.5-2.5mm2
• Yellow: AWG 12-10, 4.0-6.0mm2

Match the colour to the copper conductor size of your wire, not the overall cable diameter. For anything heavier than 6mm2, such as battery cable, use crimped or soldered lugs instead.

Solderstick colour chart

Here is the full chart for Solderstick connectors, with typical jobs for each size. The typical jobs are a guide only: always size the wire for the load and run length first, then pick the connector to match the wire.

Solderstick sizes overlap with the wire sizes most people use on 12V and 24V systems, from fine electronics wire up to 6mm2. Above that you are into battery and high-current cable, which needs lugs, not splices.

How AWG and mm2 work

You will see wire described in two ways, and it helps to understand both.

AWG (American Wire Gauge)

AWG is a numbered scale where a bigger number means a thinner wire. AWG 26 is fine electronics wire, while AWG 10 is a heavy accessory cable. Each step down the scale is a thicker wire, which is why the white connector covers 26-24 and the yellow covers 12-10.

mm2 (square millimetres)

mm2 is the cross-sectional area of the copper conductor. It is the most useful measure because it relates directly to how much copper is carrying the current. A 2.5mm2 wire has ten times the copper of a 0.25mm2 wire. Most quality cable sold in Australia lists the conductor size in mm2 somewhere on the spec sheet or packaging.

For a deeper look at choosing wire for a given load and run length, see our wire gauge guide for 12V and 4x4 wiring.

The trap with Australian auto cable sizes

This is where most people pick the wrong Solderstick size. Auto cable in Australia is often sold by a size in millimetres that is the overall diameter of the cable, not the copper area.

Narva's part numbering is a good example: the size digit in its part numbers refers to the diameter of each core in millimetres. Its 4mm single core cable has a conductor cross-section of about 1.85mm2, made up of 23 strands of 0.32mm wire, according to retailer spec listings. So a "4mm" auto cable takes a blue connector (1.5-2.5mm2), not a yellow one.

The rule is simple: find the mm2 figure for the copper, or the strand count and strand diameter, and size the connector from that. Our guide to auto cable sizes in Australia explains B&S, AWG and the overall-diameter labelling in more detail.

How to work out your wire size when it is not marked

Old looms and offcuts often have no markings. Here are three ways to work it out.

1. Check the insulation and the packaging

Many cables have the size printed along the insulation every metre or so. Look for a figure in mm2 or AWG. If you still have the packet or the invoice, the conductor size is usually listed there too.

2. Count the strands

If you know the strand count and the diameter of each strand, you can calculate the conductor area. The area of one strand is 3.14 x (strand diameter / 2) squared. Multiply by the number of strands. For 23 strands of 0.32mm: 3.14 x 0.16 x 0.16 = 0.080mm2 per strand, x 23 = about 1.85mm2. You need a micrometer or a good digital caliper to measure a single strand accurately.

3. Test fit the connector

If you have a kit, the quickest practical check is a dry fit. Strip the wire and slide the connector over it without heating. The stripped wire should slide in easily and the connector should not be loose and sloppy over the insulation. If it is very loose, go down a size. If the wire will not go in, go up a size.

Choosing a Solderstick for each size

Here is a closer look at each colour and what to watch for.

White: 0.25 to 0.34mm2 (AWG 26-24)

The white connector is for fine wire: sensors, signal and data wires, small LED leads and electronics. These wires are fragile, so strip carefully to avoid cutting strands, and keep the heat gun moving so you do not melt the thin insulation. White is also handy for repairing the small wires inside a trailer plug loom or a reversing camera lead.

Red: 0.5 to 1.0mm2 (AWG 22-18)

Red is the size most people use most often. A lot of factory wiring for lights, switches and signal circuits falls in this range, as do relay trigger wires and the power leads on many small accessories. If you are wiring a light bar on a 4x4, the switch and relay trigger side is often red, while the main power feed is usually blue or yellow.

Blue: 1.5 to 2.5mm2 (AWG 16-14)

Blue covers the next step up: accessory power feeds, driving lights and pumps, along with common auto cables such as the 4mm (1.85mm2) cable above. If you are unsure whether a cable is red or blue size, check the mm2 figure. A 1.0mm2 wire is red, a 1.5mm2 wire is blue.

Yellow: 4.0 to 6.0mm2 (AWG 12-10)

Yellow is for the heaviest splices Solderstick connectors handle, such as heavier accessory feeds and long 12V runs where the cable has been upsized to keep voltage drop down. Yellow connectors hold more solder and more copper, so they take longer to heat. Be patient and keep the heat even until the solder has fully flowed. Anything heavier than 6mm2, including battery cables and dual battery links, needs lugs, not a splice. Our dual battery guide covers those heavier connections.

Joining two wire sizes with one Solderstick

It is common to join a thin factory wire to a thicker new wire, for example when extending a lighting circuit. The general rule:

1. Choose the Solderstick size that suits the larger wire, so it fits inside the tube.
2. Check the end ring will shrink down onto the smaller wire's insulation. If the smaller wire is well below the range for that colour, the seal on that end may not grip.
3. Use the twist method or fold the thinner wire back on itself to bulk it up, so it sits firmly in the solder.

If the sizes are very different, such as a 0.5mm2 wire into a 6mm2 cable, a single splice connector is not the best tool. A small junction or terminal block, or stepping down through a fused connection, is usually a better design.

Joining three wires and wire between sizes

Three wires in one join

When you split one wire into two, the combined bundle has to fit inside the tube and the solder has to reach every strand. Add up the conductor areas on the side with two wires. If that total is above the range of the connector that suits the single wire, go up one size. Two 0.75mm2 wires, for example, add up to 1.5mm2, which points to blue rather than red. Check carefully that the two-wire end has sealed all the way around.

Wire that falls between sizes

A few cable sizes sit between the colour ranges, for example 1.25mm2 (between red and blue) or around 3mm2 (between blue and yellow). In these cases, dry fit both sizes. Use the smaller connector if the stripped wire slides in easily, because it will seal more tightly. Use the larger one if the smaller connector is a struggle to fit, because forcing wire in tends to push strands out of place.

Which kit has which sizes?

Every Solderstick kit includes all four colours, weighted towards red and blue because those are the sizes most people use.

If you go through one colour much faster than the others, a bulk 100 pack of a single colour is a cheaper way to top up.

Which should you use?

• If you are wiring sensors, LED strip leads or electronics around 0.25 to 0.34mm2, use white.
• If you are splicing switch, relay trigger, lighting or small accessory wires from 0.5 to 1.0mm2, use red.
• If you are joining accessory feeds or common "4mm" auto cable from 1.5 to 2.5mm2, use blue.
• If you are joining heavier feeds from 4.0 to 6.0mm2, use yellow.
• If you are joining two different sizes, size for the larger wire and check the smaller end seals.
• If the cable is heavier than 6mm2, or it is a battery cable, use crimped or soldered lugs and adhesive-lined heat shrink.
• If the job is 230/240V mains wiring, it needs a licensed electrician. Solderstick connectors are for low-voltage work only.

Frequently asked questions

What size solder seal connector do I need?

Match the colour to your wire's conductor 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. If you only know the AWG, white is 26-24, red is 22-18, blue is 16-14 and yellow is 12-10.

What colour solder seal connector is for 14 gauge wire?

Blue. Blue Solderstick connectors cover AWG 16-14, which is 1.5 to 2.5mm2.

What size connector for 4mm auto cable?

Usually blue. Australian "4mm" auto cable is typically labelled by its overall diameter, and Narva's 4mm cable has a conductor of about 1.85mm2, which sits in the blue range. Check the mm2 figure on your cable to be sure.

Can I use a bigger Solderstick on a smaller wire?

Only slightly. If the connector is too big, the end rings may not shrink down far enough to seal against the insulation, and the join may not be waterproof. Dry fit it first: it should not be loose over the insulation.

What is the biggest wire Solderstick connectors can join?

The yellow Solderstick connector covers up to 6.0mm2 (AWG 10). For battery cables and anything heavier than 6mm2, use crimped or soldered lugs instead of a splice connector.

Can you join two different wire sizes with a Solderstick?

Yes, if the sizes are reasonably close. Choose the connector for the larger wire, check the smaller wire's end seals properly, and twist or fold the thinner wire so it sits firmly in the solder.

Why are the connectors different colours?

The colour of the sealing rings shows the wire size range, so you can grab the right connector at a glance. It follows the same general idea as the red, blue and yellow colour coding used on many crimp terminals.

What to use

An assorted kit covers all four sizes, so you are never stuck with the wrong one. Solderstick connectors are ISO 9001 and CE certified, IP67 rated, and have been tested on video by independent reviewers including Big Clive, Electronics N More, Ross Lukeman and Samcrac.

• 50PCS kit: 10 white, 22 red, 13 blue, 5 yellow.
• 100PCS kit: 25 white, 35 red, 30 blue, 10 yellow.
• 250PCS kit: 40 white, 100 red, 90 blue, 20 yellow.
• 500PCS kit: 80 white, 200 red, 180 blue, 40 yellow.
• Bulk 100 packs of white, red, blue or yellow.
• Adhesive-lined heat shrink for lugs and heavier cable above 6mm2.

When you have the right size, our step-by-step guide to using Solderstick connectors shows you how to fit them. We ship Australia wide by Express Australia Post with free express shipping, and orders placed by 1pm are dispatched the same day.