Wiseman HSS BSP Left Hand Split Dies – British Standard Pipe Parallel LH Thread

Wiseman HSS BSP Left Hand Split Dies are manufactured from High Speed Steel (HSS) and designed for cutting new external BSP (British Standard Pipe) parallel left-hand threads, as well as repairing, cleaning and restoring damaged or worn existing threads.

These round split dies feature an adjustable design, allowing minor adjustments to the thread fit when used with a suitable die stock. They are particularly useful for specialist engineering, machinery maintenance, pipe fitting and workshop applications requiring left-hand threaded components.

BSP parallel threads, also known as BSPP or G threads, feature a 55° Whitworth thread profile with rounded crests and roots. Unlike BSPT (British Standard Pipe Taper) threads, BSP parallel threads maintain a constant diameter along the threaded section.

Unlike standard right-hand threads, left-hand BSP threads tighten anticlockwise and loosen clockwise. These reverse-threaded connections are used in specialist equipment and mechanical assemblies where left-hand threads are required by the original design.

BSP parallel threads are commonly used in hydraulic, pneumatic and industrial fittings. Where a pressure-tight connection is required, sealing is normally achieved using a suitable washer, O-ring, gasket or other sealing arrangement rather than the parallel threads themselves.

These split dies are suitable for producing and restoring left-hand BSP parallel external threads on compatible pipes, fittings, adapters and other threaded components.

Key Features

• High Speed Steel (HSS) – Durable construction for reliable thread cutting and maintenance.

• BSP Parallel Thread Form – Designed for British Standard Pipe Parallel external threads.

• Left Hand Thread – Tightens anticlockwise and loosens clockwise.

• Adjustable Split Design – Allows minor adjustment of the thread fit when used with a suitable die stock.

• Round Die Construction – Designed for use with compatible die stocks and die holders.

• 55° Whitworth Thread Profile – Features rounded crests and roots.

• Parallel Thread Design – Produces threads with a constant nominal major diameter along their length.

• Thread Cutting & Restoration – Suitable for cutting new external threads and repairing existing threads.

• Specialist Engineering Applications – Suitable for equipment requiring left-hand BSP parallel threads.

Applications

Suitable for:

• Cutting new BSP parallel left-hand external threads.

• Repairing damaged or worn BSP left-hand threads.

• Cleaning and restoring existing external threads.

• Manufacturing specialist left-hand threaded pipe fittings.

• Hydraulic fittings and adapters requiring BSP LH threads.

• Pneumatic equipment and industrial machinery.

• Mechanical assemblies requiring reverse-threaded connections.

• General engineering and workshop machining.

• Manufacturing replacement left-hand threaded components.

Recommended Use

Select the correct BSP left-hand split die size and threads per inch (TPI) to match the required external thread.

BSP sizes are designated by nominal pipe sizes rather than the actual outside diameter of the thread. For example, a 1/2" BSP thread has an external major diameter of approximately 20.96mm, not 12.7mm.

Secure the die in a compatible die stock or holder, ensuring the adjustment screws are correctly positioned. Prepare the workpiece to the appropriate diameter and apply a suitable chamfer to help the die start squarely.

Apply a suitable cutting lubricant and rotate the die anticlockwise to cut the left-hand thread, viewed from the starting end of the workpiece. Periodically reverse the die clockwise slightly to help break and clear chips where appropriate for the material and cutting conditions.

The adjustable split design allows minor adjustments to the thread fit. Check the finished thread using a suitable BSP parallel left-hand thread gauge or correctly specified mating component.

Where the threaded connection is required to seal against pressure, ensure that the appropriate sealing method is used and that the complete connection is suitable for the intended application.

Important

• Suitable for BSP (British Standard Pipe Parallel) left-hand external threads only.

• Left-hand threads tighten anticlockwise and loosen clockwise.

• Not suitable for cutting standard right-hand BSP threads.

• Features a 55° Whitworth thread profile.

• Produces parallel threads, not tapered threads.

• Not interchangeable with BSPT or NPT dies.

• BSP nominal thread sizes do not correspond directly to the measured external thread diameter.

• BSP parallel threads generally require a separate sealing arrangement where a pressure-tight connection is needed.

• Adjustable round split die for cutting and restoring external threads.

• Requires a compatible die stock or die holder.