Guides / Process
Threading and Tapping Tungsten: What Is Different From Steel
Updated September 26, 2026 · Reviewed September 26, 2026
Threaded features are routine on most machined parts, but tungsten’s behavior under a tap varies sharply by grade. This guide covers what to expect, when to design around a thread rather than force one, and what to put on the drawing so your shop can flag risk before it becomes a scrapped part.
Heavy alloy: routine, with faster tool wear
Tungsten heavy alloy taps in a way broadly similar to a hard steel. Standard taps, run at appropriate speeds with coolant, cut clean threads across most common sizes. The main practical difference from steel is tool wear: the abrasive tungsten grains in the microstructure wear tap edges faster than steel does, so shops replace taps more often on heavy alloy work, which is reflected in the cost of the operation but does not change what is achievable.
Fine threads and thin-walled tapped bosses in heavy alloy need the same care they would in any hard, dense metal: adequate wall thickness around the thread to avoid deformation or cracking under tapping stress, and attention to thread engagement length so the joint has enough strength for its application.
Pure tungsten: proceed with caution
Pure tungsten’s brittleness makes tapping a higher-risk operation than it is in heavy alloy. The radial stress a tap applies to the surrounding material can chip thread crests or crack a thin-walled boss, particularly on fine threads and smaller diameters where there is less material to absorb the stress. This does not mean tapping pure tungsten is never done, but it means the feature needs deliberate design attention rather than being treated as a routine detail.
Shops that do tap pure tungsten successfully typically use generous wall thickness around the threaded feature, moderate thread pitch rather than the finest available, and controlled tapping parameters to minimize stress on the surrounding material.
Designing around the risk
When a threaded feature in pure tungsten is high risk or simply not practical, a few alternatives are worth considering at the design stage rather than after a part has cracked in production:
- Move the fastener location to a heavy alloy component, if the assembly allows it, so the pure tungsten part carries no threaded feature at all.
- Increase the wall thickness around the boss, giving the material more cross-section to absorb tapping stress, at the cost of some added mass and machining time.
- Use a different attachment method, such as a clamped joint, a retaining feature, or a bonded interface, that achieves the mechanical connection without a threaded hole directly in the brittle material.
- Insert a heavy alloy bushing into the pure tungsten part specifically to carry the thread, isolating the threaded feature from the brittle material entirely.
- Consider a wire or helical thread insert, which spreads the load over a longer engagement and reduces the peak stress compared with a thread cut directly into the boss.
Tungsten copper and tungsten carbide
Tungsten copper, with its more ductile behavior from the copper phase, taps more like heavy alloy than like pure tungsten, and threaded features are routine on tungsten copper electrodes and contacts. Tungsten carbide is a different case entirely: sintered carbide is not tapped after firing, since it is too hard for standard tap geometry. Any threaded feature in a carbide part is either machined before sintering, in the softer green state, or achieved through a separate mechanical fastening approach rather than a direct tapped thread in the fired material.
Practical thread sizing guidance
As a general rule across grades, larger thread sizes and coarser pitches tolerate the tapping process better than fine threads on small diameters, since they leave more material to resist the radial stress of the tap. If your design allows flexibility in thread size, favor the larger, coarser option where function permits, particularly on pure tungsten.
Thread risk by grade and feature
The table below is a general guide, not a guarantee for every geometry. Wall thickness, hole depth and the specific alloy all affect what a given shop can actually achieve.
| Grade | Coarse thread, thick boss | Fine thread, thin boss | Typical approach |
|---|---|---|---|
| Heavy alloy (W-Ni-Fe or W-Ni-Cu) | Routine | Possible with care | Standard tap, faster tap wear than steel |
| Tungsten copper | Routine | Routine | Standard tap, behaves like a hard copper alloy |
| Pure tungsten | Possible with generous wall thickness | High risk, avoid or redesign | Careful tapping, insert, or ground thread |
| Tungsten carbide (sintered) | Not tapped after sintering | Not tapped after sintering | Machine thread before sintering, or use a separate fastening method |
What shops check before quoting a threaded tungsten part
A shop looking at a drawing with a tapped hole in tungsten is usually checking three things: the grade and whether it is pure tungsten or an alloy, the wall thickness around the boss relative to the thread size, and how deep the engagement needs to be. Answering these on the drawing itself, rather than leaving the shop to ask, is the fastest way to get a quote that already accounts for the risk rather than pricing it in as a contingency.
A shop that has tapped pure tungsten before will often ask a fourth question that is easy to miss: whether the thread is load-bearing in normal use or only holds a cover, fastener or light fitting. A lightly loaded thread gives the shop more room to choose a conservative approach, such as a coarser pitch or an insert, without a conversation about redesigning the joint. A structural thread on a brittle material is a different, more careful conversation, and it is worth having it before the drawing is finalized rather than after a quote comes back higher than expected.
Specifying threaded features on your drawing
- State the grade clearly, since threading risk and approach differ significantly between heavy alloy and pure tungsten.
- Call out wall thickness around any threaded boss, especially on pure tungsten, so the shop can flag a risky feature before machining rather than during it.
- Note any load or torque requirement on the joint, so the shop understands what the thread actually needs to hold.
- State the required engagement length, rather than assuming maximum depth, so the shop is not tapping deeper than the joint actually needs.
- Ask your shop directly about pure tungsten threaded features before finalizing the drawing, since this is one area where shop-specific experience varies more than most.
See our guide on how to machine tungsten for where threads fit among tools, finishing and joining.
When your drawing is ready, send your RFQ and we match it with shops experienced in your grade. For a broader look at features that raise cost or risk across tungsten grades, see common mistakes when specifying a tungsten part. For what each grade generally allows, see what each tungsten grade allows.
Frequently asked questions
Can tungsten heavy alloy be tapped like steel?
Yes, in most sizes. Standard taps cut heavy alloy threads reliably, with faster tool wear than in steel because of the material's abrasiveness. Fine threads and thin-walled tapped bosses need more care, the same as they would in a hard steel.
Why is tapping pure tungsten risky?
Pure tungsten is brittle, and the radial stress a tap puts on the surrounding material can crack a thin section or chip the thread crest, especially on fine threads or small diameters. Shops often avoid tapping pure tungsten directly for these features.
What is the alternative to tapping a hole in pure tungsten?
Common alternatives include using a heavier-walled boss to reduce cracking risk, switching the fastener location to a heavy alloy insert or adjacent part, or using a different attachment method, such as a clamped or bonded joint, that does not require a threaded feature directly in the pure tungsten.
Do thread inserts help on tungsten parts?
Sometimes. A helical wire insert or a solid bushing installed in a properly sized and chamfered hole can spread load more evenly than a thread cut directly into brittle material, but the hole preparation still matters. Ask your shop whether an insert makes sense for your specific boss geometry rather than assuming it solves every case.
Can a thread be ground into tungsten instead of tapped?
For critical or very fine threads, some shops finish threads by grinding rather than tapping, particularly on pure tungsten or tungsten carbide. This is slower and costs more than tapping but avoids the radial stress a tap applies.
Does thread depth matter more on tungsten than on steel?
Engagement length matters on any material, but on tungsten it is worth confirming explicitly, since a shorter, over-engineered thread reduces the stress applied during tapping compared with chasing maximum depth on every hole.
Sources
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