Short definition
Solder wire is the filler metal supplied as a coiled wire on a spool, melted by a torch into a fluxed copper joint to form a sweated connection. Modern residential standard is 95% tin / 5% antimony (Sb5), supplied as 1/2 lb or 1 lb spools. For the regulatory and code framing, see lead-free solder.
What it is
Solder wire is the form factor; lead-free is the regulatory category. ASTM B32 covers the alloy specification. Standard residential wire diameters are 0.062 inch (1.5 mm) for most copper work, 0.125 inch (3 mm) for larger pipe. A 1/2-lb spool is enough for roughly 50 1/2-inch joints.
Solder bar (1-lb ingots) is for industrial dipping and wiping — not residential plumbing. Solder paste is for surface-mount electronics and has no plumbing use.
Why it matters to a homeowner
For DIY soldering, buy a 1/2-lb or 1-lb spool of 95/5 lead-free, tape the loose end after each use, and store it in a dry indoor location. A spool left in a hot truck or shed oxidizes and won’t tin properly. Wire dropped on a dirty floor picks up debris that won’t melt — cut off the dirty section.
Premium tin-silver lead-free (Sn96.5/Ag3.5) flows slightly cleaner at 2 to 3 times the cost. It’s not necessary for residential — 95/5 tin-antimony is the standard.
Common variants and not the same as
- Solder wire vs. lead-free solder. Same product; “solder wire” describes the form factor, “lead-free” describes the regulatory category. See lead-free solder for full coverage.
- Solder wire vs. brazing rod. Brazing rod is silver-bearing, melts above 840°F. Different alloy category. See brazed copper joint.
- Solder wire vs. solder paste. Paste is for electronics surface-mount work, not plumbing.
Common failure modes
- Spool left in a hot truck. Surface oxidizes, won’t tin properly.
- Wire dropped on dirt. Won’t flow until you cut off the contaminated section.
- Wrong alloy on potable water. Must be lead-free per SDWA. Read the spool label.