BRITISH STANDARD WHITWORTH BSW TAPS

Sutton Tools manufactures high-quality British Standard Whitworth (BSW) taps available as individual intermediate hand taps, 3-piece sets, or comprehensive tap and die sets. They offer two primary material grades: Carbon/Tungsten Chrome Alloy for light maintenance and general-purpose DIY, and High-Speed Steel (HSS) for heavy-duty industrial thread cutting.

British Standard Whitworth (BSW) is an imperial, inch-based screw thread standard established in 1841 by Sir Joseph Whitworth. It is historically significant as the world's first national screw thread standard.

• 55-Degree Flank Angle: The V-shaped grooves of the thread meet at an included angle of exactly 55 degrees. This makes it shallower than modern Metric and American Unified threads, which use a 60-degree angle.
• Rounded Crests and Roots: Both the peaks (crests) and valleys (roots) of the thread are perfectly radiused and rounded. This smooth design prevents stress concentration points, making BSW threads highly resistant to metal fatigue in heavy machinery. 
• Coarse Pitch: BSW is a coarse thread series. It features fewer threads per inch (TPI) than "fine" thread standards, allowing it to be cross-threaded less easily and assembled rapidly in heavy industrial environments.

• Decimal Equivalent: Exactly 0.125 inches.
• Metric Equivalent: Approximately 3.175 millimeters.

• Because it is a small 1/8" diameter, 40 TPI is considered a coarse pitch relative to its size.
• Thread Pitch: The actual physical distance from one thread peak to the next is 1 Divided by 40 = 0.025 inches (0.635 mm).

• 55° Flank Angle: The V-grooves slope inward at a 55-degree angle.
• Rounded Profile: The crests (peaks) and roots (valleys) are distinctly radiused to smooth out stress points.

TYPES OF TAPS

• Design: Features a long, gradual chamfer at the tip covering the first 7 to 10 threads.
• Purpose: Used to start the threading process. The long taper allows the tool to easily enter the drilled hole, align straight, and gently begin cutting the first shallow groove.
• Limitation: It cannot cut a complete thread to the bottom of a hole because the tip is narrow and lacks full-sized cutting teeth.

• Design: Features a shorter chamfer at the tip covering the first 3 to 5 threads.
• Purpose: Used after the Taper tap to cut the threads deeper and closer to full size. In a "through-hole" (a hole drilled all the way through the metal), an Intermediate tap is often the final tap needed to finish the job.
• Note on Terminology: In the UK, Australia, and BSW standards, this is widely called an Intermediate tap. In the US, it is commonly referred to as a Plug tap.

• Design: Features a very short chamfer at the tip covering only 1 to 2 threads. The rest of the tap features full-sized, sharp cutting teeth.
• Purpose: Used exclusively to finish "blind holes" (holes that stop mid-way through the metal and do not go all the way through). It allows you to cut full, usable threads right down to the very bottom floor of the hole.
• Limitation: Never use this tap to start a hole. Because it has no guiding taper, it will wobble, cross-thread, or immediately snap under the sudden cutting pressure.