HSS Adjustable Split Dies for External Thread Cutting
Explore our range of High Speed Steel (HSS) Split Dies, designed for cutting new external threads and repairing or restoring existing threads on bolts, rods, studs and other threaded components.
Our range includes Metric Coarse, Metric Fine, UNC, UNF, UNEF, UNS, UNJF, BSW, BSF, BSB, BA, Model Engineer Whitworth, BSCY and BSP thread forms, together with specialist left-hand threading dies.
Manufactured from High Speed Steel, these round split dies are suitable for general engineering, precision machining, automotive repairs, machinery maintenance, fabrication and restoration work.
Unlike solid die nuts, adjustable split dies feature a split in the die body, allowing minor adjustments to the thread fit when used with a compatible die stock or die holder.
Whether you are producing new external threads or restoring damaged threads, our selection of metric and imperial split dies provides solutions for a wide range of engineering applications.
Available Split Die Thread Types
Metric Split Dies
Metric Coarse (M)
Metric Coarse split dies are designed for cutting standard ISO metric external threads. They feature a 60° thread profile and are widely used in engineering, manufacturing, automotive repairs and general machinery maintenance.
Metric Fine (MF)
Metric Fine split dies feature the same 60° ISO metric thread profile but use a finer pitch than Metric Coarse threads of the same diameter. They are commonly used in precision engineering, automotive components and specialist mechanical assemblies.
Unified Thread Split Dies
UNC – Unified National Coarse
UNC split dies are designed for cutting Unified Coarse external threads with a 60° thread profile. Commonly used in machinery, industrial equipment and general engineering applications.
UNF – Unified National Fine
UNF split dies are suitable for producing finer-pitch Unified external threads, commonly found in automotive engineering, machinery and precision mechanical components.
UNEF – Unified National Extra Fine
UNEF split dies are designed for extra-fine Unified threads used in specialist engineering applications requiring finer thread pitches.
UNJF – Unified National J-Series Fine
UNJF split dies are designed for the specialist Unified J-Series thread form, which features a controlled external root radius to reduce stress concentrations. Used in aerospace and other high-performance engineering applications where the relevant specifications permit die-cut threads.
UNS – Unified National Special
UNS split dies are suitable for special Unified thread diameter and pitch combinations outside the standard UNC, UNF and UNEF series.
British Standard & Whitworth Split Dies
BSW – British Standard Whitworth
BSW split dies feature a 55° Whitworth thread profile with rounded crests and roots. Commonly used for maintaining older British machinery, vintage vehicles and traditional engineering equipment.
BSF – British Standard Fine
BSF split dies use a finer-pitch Whitworth thread form, making them particularly useful for classic vehicle restoration, machinery maintenance and traditional British engineering applications.
BSB – British Standard Brass
BSB split dies are designed for British Standard Brass threads, traditionally featuring a 55° thread profile and 26 threads per inch. Commonly used for brass fittings, instruments and specialist engineering components.
BA – British Association
BA split dies feature a distinctive 47.5° thread profile and are available in numbered thread sizes. They are particularly useful for model engineering, electrical equipment, instruments and small precision components.
ME – Model Engineer Whitworth
Model Engineer split dies feature a 55° Whitworth thread profile and commonly use fine pitches of 32 or 40 TPI. Suitable for model steam engines, miniature machinery and specialist model engineering applications.
BSCY – British Standard Cycle
BSCY split dies are designed for British Standard Cycle threads, also known as CEI threads. Featuring a 60° thread profile, they are particularly useful for classic bicycle and vintage British motorcycle restoration.
BSP Pipe Thread Split Dies
BSP – British Standard Pipe Parallel
BSP split dies are designed for cutting parallel external pipe threads with a 55° Whitworth profile. Commonly used for hydraulic fittings, pneumatic connections, pipe fittings and industrial machinery.
Left Hand Split Dies
Our range also includes specialist Left Hand Split Dies, designed for producing external threads that tighten anticlockwise rather than clockwise.
Available thread forms include:
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UNC Left Hand – Unified National Coarse
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UNF Left Hand – Unified National Fine
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BSW Left Hand – British Standard Whitworth
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BSF Left Hand – British Standard Fine
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BA Left Hand – British Association
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BSP Left Hand – British Standard Pipe Parallel
Left-hand threads are commonly specified for rotating assemblies, specialist fasteners, machinery components and applications requiring reverse-threaded connections.
Why Choose HSS Split Dies?
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High Speed Steel Construction – Suitable for thread cutting across a range of machinable engineering materials.
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Adjustable Split Design – Allows minor adjustment of the thread fit using a compatible die holder.
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New Thread Cutting – Suitable for producing external threads on appropriately prepared workpieces.
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Thread Repair & Restoration – Useful for cleaning and restoring damaged or worn external threads.
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Metric & Imperial Options – A wide selection of thread forms and pitches.
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Right Hand & Left Hand Threads – Options for standard and reverse-threaded applications.
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Workshop Versatility – Suitable for engineering, maintenance, fabrication and restoration.
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Multiple Thread Sizes – Choose the appropriate diameter and pitch for your application.
Split Dies vs Die Nuts – What's the Difference?
Split Dies
Round adjustable split dies are primarily designed for cutting new external threads. Their split construction allows minor adjustment of the thread fit, making them suitable for thread production as well as restoration.
Die Nuts
Hexagon die nuts are generally used for cleaning, chasing and restoring existing external threads. They are typically fixed in size and are not intended as the primary tool for cutting full-depth new threads.
For producing new external threads, an appropriately specified HSS split die is generally the preferred option.
Choosing the Correct Split Die
When selecting a split die, it is important to identify the correct:
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Thread Type – Metric, UNC, UNF, BSW, BSF, BA, BSP or another thread series.
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Thread Diameter – The nominal outside diameter of the thread.
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Thread Pitch – Specified in millimetres for metric threads or threads per inch (TPI) for imperial threads.
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Thread Direction – Right hand or left hand.
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Die Outside Diameter – The physical outside diameter of the die, which must fit the selected die stock or holder.
Different thread forms are not necessarily interchangeable, even when their nominal diameters or thread pitches appear similar.
For best results, use the correct die holder, prepare the workpiece to the appropriate diameter, apply suitable cutting lubricant and check the finished thread using an appropriate thread gauge.
