If you are buying empty socket line (bulk spools) to customize your Christmas display this year, you’ve likely run into two cryptic codes: SPT-1 and SPT-2.

They look almost identical in photos. They both typically use 18-gauge copper wire. They both carry electricity just fine.

So, what is the difference, and which one should you buy?

The difference isn't in the wire itself—it’s in the jacket.

1. What do the numbers mean?

Think of the "SPT" rating like a winter coat for your wire.

• SPT-1: This is the standard "jacket." The insulation is thinner (about 0.030 inches thick).

• SPT-2: This is the heavy-duty "parka." The insulation is thicker (about 0.045 inches thick).

Important Note: In most cases, both wires contain the same amount of copper (18 AWG). SPT-2 does not necessarily carry more electricity; it just has better protection against the elements.

2. When to choose SPT-1 (The Residential Standard)

For 95% of homeowners, SPT-1 is the correct choice.

• Pros: Because the insulation is thinner, the wire is more flexible, lighter, and easier to lay flat against your fascia boards. It is also slightly less expensive.

• Best For: Outlining rooflines, wrapping trees, and general seasonal decoration in moderate climates.

3. When to choose SPT-2 (The Commercial Tank)

If SPT-1 is the Honda Civic, SPT-2 is the Humvee.

• Pros: The thicker insulation resists UV fading and physical damage better. It can handle colder temperatures without becoming brittle and cracking.

• Best For: Professional installers who re-use wire for 5+ years, commercial displays that stay up for months, or displays in areas with extreme winter weather/high foot traffic.

4. The Golden Rule: Don't Mix Your Plugs!

This is the most critical part of this guide.

Because SPT-2 wire is physically thicker, you must buy plugs that match your wire.

• If you buy SPT-1 Wire: You must use SPT-1 Plugs (Gilbert aka Vampire Plugs).

• If you buy SPT-2 Wire: You must use SPT-2 Plugs.

Why? If you try to use an SPT-1 plug on SPT-2 wire, the channel will be too narrow, and you might cut through the insulation or break the plug. If you use an SPT-2 plug on SPT-1 wire, the fit will be too loose, and the connection might fail or arc.

The Verdict

• Most Homeowners: Stick with SPT-1. It’s easier to handle, cheaper, and more than durable enough for seasonal use.

• Commercial/Extreme Weather: Upgrade to SPT-2 for that extra layer of protection.

Just remember: Match your plug to your wire. If you do that, you can’t go wrong.