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When a Copper Part Should Use a Thread Insert

September 26, 2026

Tapping is the operation where pure copper parts get scrapped. The tap loads up, the thread tears, and a broken tap at the last step turns a finished part into swarf. Inserts are one of three answers, and they solve a different problem from the other two.

Three answers to a copper thread

Change the grade. C14500 or C14700 taps cleanly. If the drawing allows a free-machining grade, this is the cheapest fix. See C110 vs C145.

Thread mill instead of tap. Avoids the broken tap risk and produces a cleaner form in pure copper. Slower per hole, and it does nothing about the softness of the thread once it exists.

Use an insert. A helical wire insert or a solid threaded bushing in a harder material, installed in a tapped or bored hole. This is the only answer that addresses wear.

When an insert is the right call

• The joint is assembled and disassembled repeatedly. Copper threads deform with each cycle.
• A steel bolt is torqued into copper. Galling and thread stripping are real at busbar torque values.
• The thread is small relative to the load, and the copper cannot hold the pull-out.
• The part must stay on pure copper for conductivity or vacuum reasons, so a grade change is not available.

When it is not

• One-off or rarely disturbed assemblies, where a tapped thread in copper is adequate.
• Vacuum components, where an insert is a trapped volume and a contamination source unless it is specifically a vented vacuum grade insert.
• Where the thread carries current and the insert material would add resistance at the interface.
• Where the extra operation and part cost is not justified by the load.

Helical wire against solid inserts

Helical wire inserts are cheap, need a special tap, and suit most general fastening. Solid inserts, threaded bushings, are more expensive, easier to install with standard tooling, and better where the joint sees vibration or high torque.

For busbar joints specifically, the usual practice is a through bolt with a nut, which avoids the question entirely. Where a blind thread in copper is unavoidable, a solid insert is the safer choice.

What to put on the drawing

M8 x 1.25 helical insert, [length] x d,
installed per manufacturer's instructions.
Tap drill per insert manufacturer.

Or, if you would rather let the shop decide:

M8 thread, repeated assembly, steel bolt.
Insert or thread mill at shop's discretion.
Pure copper required for conductivity, no grade substitution.

That second version tells the shop what matters and lets it pick the cheapest route that meets it. How to specify copper on a drawing covers the rest of the callout.

What it costs

An insert is a second operation and a purchased part. On a copper part it often pays for itself by removing the tap scrap risk. Ask for the quote both ways if you are unsure. Design rules for machined copper parts covers thread depth, which is the other lever.

Frequently asked questions

Keep reading

• Copper Alloy Inserts in Injection Molds: What They Cool and What They Cost
• Machined Copper Induction Coils: Skin Depth, Cooling and Joints