Buy Die Nuts Online in Australia
Die Nut Sizes — Quick Reference
Die nuts are hex-form threading dies driven by a standard spanner — their primary use is rethreading and chasing damaged external threads, not cutting new threads from scratch (round split dies do that better). AIMS stocks die nuts in HSS and carbon steel across metric, imperial, BSP and BSW thread forms. Match thread form to the existing thread on the workpiece.
| Thread Form | Pitch Standard | Common Workshop Sizes | Typical Use |
|---|---|---|---|
| Metric Coarse | ISO 261 / AS 1721 | M3, M4, M5, M6, M8, M10, M12, M14, M16, M20, M24 | General Australian + European fastener rethreading |
| Metric Fine | ISO 262 / AS 1721 | M8×1.0, M10×1.25, M12×1.25, M14×1.5, M16×1.5, M20×1.5 | Automotive, hydraulic fittings, precision fine-pitch |
| UNC (Unified Coarse) | ASME B1.1 | 1/4"-20, 5/16"-18, 3/8"-16, 7/16"-14, 1/2"-13, 5/8"-11 | US-origin machinery rethreading, older equipment |
| UNF (Unified Fine) | ASME B1.1 | 1/4"-28, 5/16"-24, 3/8"-24, 7/16"-20, 1/2"-20 | Aerospace, precision automotive, fine-pitch repair |
| BSW (Whitworth) | BS 84 | 1/4", 5/16", 3/8", 7/16", 1/2", 5/8", 3/4" | Older Australian/UK machinery, vintage equipment |
| BSP (Pipe Thread) | BS 21 / ISO 228 | 1/8", 1/4", 3/8", 1/2", 3/4", 1" | Hydraulic and pneumatic pipe thread chasing |
For cutting new threads from scratch, use a round split die with a die stock — it allows adjustment for clean shoulder threading. For damaged INTERNAL threads, use a tap instead. Companion ranges: threading tools, tap & die sets, tap wrenches.
Die Nuts
Die nuts are hexagonal-form threading dies that can be driven by a standard open-end spanner or adjustable wrench. Unlike round split dies, die nuts do not allow diameter adjustment — they cut a fixed, standard thread form. Their primary application is rethreading and chasing damaged external threads rather than cutting new threads from scratch. AIMS Industrial supplies die nuts in metric and imperial thread forms, in HSS and carbon steel.
Die Nuts vs Round Split Dies
Round split dies in a die stock are the correct tool for cutting new external threads from bar stock — they can be adjusted to take a roughing cut, then closed to take a finishing cut for a clean, accurate thread. Die nuts provide no adjustment and are harder to start precisely on a plain bar. Where die nuts excel is in rethreading applications: the hex body allows them to be placed on a damaged bolt or stud and worked along it with a spanner to clean up burred or corroded threads without the need for a die stock. For maintenance applications where rethreading fasteners in-situ is the primary task, die nuts are faster and more convenient than round dies.
Thread Specifications
Metric die nuts are available from M3 through M24 in standard pitch (coarse) and fine pitch configurations. Imperial die nuts cover BSW (British Standard Whitworth), BSF (British Standard Fine), and UNC/UNF thread forms — relevant for older Australian and American equipment that uses imperial threads. Always confirm the thread form and pitch before selecting a die nut; metric coarse and fine at the same nominal diameter look similar but are incompatible.
HSS vs Carbon Steel
HSS die nuts maintain their cutting edge longer and are preferred for production use and for harder materials. Carbon steel die nuts are an economical choice for occasional maintenance rethreading on mild steel fasteners. For stainless steel or hardened fasteners, HSS is the minimum specification.
Thread Classes and Fit
Threading standards define different fit classes for the clearance between external and internal thread profiles — a tighter fit class produces less slop in the assembled joint but requires more precise cutting. Die nuts cut to standard tolerance and are suited to general-purpose thread repair and maintenance where the original thread was itself to standard tolerance. For precision or close-tolerance threading work, a round split die in a die stock, with diameter adjustment, is the more appropriate tool. Die nuts are correctly viewed as a maintenance tool for restoring damaged standard-tolerance fastener threads rather than a precision thread-cutting instrument. For guidance on die nut selection for your application, contact our team.
People Also Ask — Die Nuts
Q: What is a die nut?
A die nut is a hexagonal-form threading die driven by a standard open-end spanner or adjustable wrench. Unlike round split dies, die nuts provide no diameter adjustment — they cut a fixed, standard thread form and are primarily used for rethreading and chasing damaged external threads rather than cutting new threads from scratch on plain bar stock.
Q: What is the difference between a die nut and a round split die?
A round split die in a die stock can be adjusted to take a roughing cut followed by a finishing cut — the preferred method for cutting new threads on bar stock. A die nut provides no adjustment, making it harder to start on a plain bar. Die nuts excel at rethreading: placed over a damaged bolt or stud, they can be worked along it with a spanner to restore a corroded or burred thread without a die stock.
Q: What thread forms are available in die nuts?
Die nuts are available in metric coarse (ISO 261), metric fine (ISO 262), UNC (Unified Coarse), UNF (Unified Fine), BSW (Whitworth), and BSP (British Standard Pipe) thread forms — covering Australian, European, US and legacy British thread standards for both fastener and pipe thread rethreading work.
Q: When should an HSS die nut be used instead of a carbon steel die nut?
HSS (high-speed steel) die nuts provide greater hardness and wear resistance — suited for harder materials such as alloy steels and stainless, high-volume rethreading work, and applications where longer tool life justifies the higher cost. Carbon steel die nuts suit occasional light-duty rethreading on mild steel and standard fastener materials.
Q: Can die nuts be used to repair damaged BSP pipe threads?
Yes. BSP die nuts in standard pipe sizes are used to chase and restore damaged external BSP threads on pipe ends, hydraulic fittings, and plumbing connections — restoring a clean thread without cutting a new one from bare material. This is a common maintenance operation when hydraulic or pneumatic fittings have been over-tightened or cross-threaded.
Q: How do I use a die nut to chase a damaged thread?
Clean the thread and apply cutting oil, then start the die nut by hand at the good end and work it down over the damaged section with a spanner, backing off a half-turn now and then to clear chips. Let it follow the existing thread rather than forcing a new path, and keep it square to the bolt. The aim is to restore the original thread, not to cut a deeper one.
Q: Can a die nut cut a brand-new thread on plain bar?
It can start one in soft material at a pinch, but it's the wrong tool: with no diameter adjustment it's hard to start square and tends to cut oversize or drunken threads. Use a round split die in a die stock for new threads, where you can take a roughing then a finishing cut. Keep die nuts for rethreading and cleaning up existing threads.
Q: How do I identify the thread on a damaged bolt before ordering a die nut?
Measure the outside diameter with calipers and the pitch with a thread pitch gauge (or count threads over 25mm for imperial). That tells you the diameter and whether it's metric coarse, metric fine, UNC, UNF, BSW, or BSP. Matching both diameter and pitch matters — M10 x 1.5 and M10 x 1.25 look alike but won't chase each other's threads.
Q: Do I need cutting fluid when using a die nut?
Yes on steel and stainless. Cutting fluid keeps the die cool, gives a cleaner thread, and stops the die picking up material and tearing the thread; on stainless it also reduces work-hardening. Aluminium and brass can be chased dry or with a light oil. A standard tapping or threading compound is fine — the same fluids you'd use for taps and round dies.
Q: Are hex die nuts and round dies interchangeable?
They cut the same thread form but do different jobs. A hex die nut is driven by a spanner and is meant for rethreading in the field; a round split die needs a die stock and is meant for cutting and adjusting threads. Many tap-and-die sets include one or the other; if you do a lot of thread repair, a set of hex die nuts alongside your round dies covers both tasks.