Wiseman HSS BSW Left Hand Split Dies – British Standard Whitworth LH Thread

Wiseman HSS BSW Left Hand Split Dies are manufactured from High Speed Steel (HSS) and designed for cutting new external BSW (British Standard Whitworth) 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 general engineering, machinery maintenance, restoration and specialist workshop applications requiring left-hand threaded components.

BSW threads feature a 55° Whitworth thread profile with rounded crests and roots. British Standard Whitworth is a traditional imperial thread system widely used in older British machinery, vintage vehicles, agricultural equipment and engineering assemblies.

Unlike standard right-hand threads, left-hand BSW threads tighten anticlockwise and loosen clockwise. They are used in applications where the direction of rotation, mechanical movement or equipment design requires a reverse-threaded fastening.

These split dies are suitable for producing and restoring left-hand BSW threads on bolts, studs, rods, shafts and other externally threaded components.

Key Features

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

• BSW Thread Form – Designed for British Standard Whitworth 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.

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

• Reverse Thread Applications – Suitable for components requiring left-hand threaded fastenings.

• Engineering & Restoration Use – Suitable for general machining, machinery maintenance and vintage equipment restoration.

Applications

Suitable for:

• Cutting new BSW left-hand external threads on rods, bolts and studs.

• Repairing damaged or worn BSW left-hand threads.

• Cleaning and restoring existing external threads.

• Manufacturing left-hand threaded shafts and fasteners.

• Maintenance of older British machinery and equipment.

• Vintage and classic vehicle restoration.

• Agricultural machinery repairs.

• Rotating assemblies requiring reverse-threaded fastenings.

• General engineering and workshop machining.

• Manufacturing replacement left-hand threaded components.

Recommended Use

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

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. For accurate results, check the finished thread using a suitable BSW left-hand thread gauge or correctly specified mating component.

Ensure that the die is started squarely and that the correct cutting direction is maintained throughout the operation.

Important

• Suitable for BSW (British Standard Whitworth) left-hand external threads only.

• Left-hand threads tighten anticlockwise and loosen clockwise.

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

• Features a 55° Whitworth thread profile with rounded crests and roots.

• Not interchangeable with BSF, UNC, UNF, metric or other thread forms.

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

• Requires a compatible die stock or die holder.

• Ensure the correct nominal diameter and TPI are selected before use.