A special radius tap is a made-to-order tap ground with a non-standard radius on the thread root, crest or form, built to your drawing or sample rather than pulled from a catalog. When a print calls for a controlled radius that standard stock taps can’t produce, a special radius tap is how you cut that thread correctly the first time. This guide covers what these taps are, when you need one, which thread forms and substrates suit them, and what to send a manufacturer to get a quote.
What Are Special Radius Taps?
A special radius tap is a custom tap whose cutting profile is ground to a specified radius at the thread root, crest or flank, so the finished thread matches a non-standard form. Instead of the generic profile found on catalog taps, the geometry is built around your part’s requirements.
The radius matters because the thread root is where stress concentrates. A sharp root corner acts as a notch under load, and in cyclic or high-load service that notch is where fatigue cracks tend to start. A controlled root radius spreads stress over a larger area, which supports fatigue resistance and strength in the finished thread. That’s why prints for critical fasteners and load-bearing threaded features often call out a radius explicitly.
Special radius taps sit within the broader family of special thread taps, the made-to-order taps Taylor Tool manufactures for thread forms and requirements that general suppliers don’t stock. The distinction is the angle: this page focuses on the radius itself, while the broader category covers custom pitches, forms and sizes generally. A standard catalog tap is designed for a common, published thread profile; a special radius tap is designed for your profile.
When Do You Need a Special Radius Tap Instead of a Standard Tap?
You need a special radius tap when your print specifies a radius, thread form or pitch that standard stock taps cannot produce. If a catalog tap can’t hold the geometry on the drawing, a custom tool is the only reliable route.
Common situations include:
- Fatigue-critical threads. Aerospace and power generation components often see cyclic loading, where root geometry directly affects service life.
- Unusual or proprietary thread forms. Some assemblies use a modified or company-specific profile with no stocked tap.
- Replacement or repair work. When you have a sample part but no standard designation, a tap can be matched to the sample.
- Tight performance targets. When a standard thread works but a modified radius improves strength or fit, a modified standard may be enough.
Taylor Tool builds both ends of the spectrum: a modified standard tap, or a completely unique tool. For related made-to-order work beyond radius requirements, see special purpose taps. So how is a special radius tap different from a standard tap? A standard tap follows a published profile and is available off the shelf; a special radius tap is ground to a specific radius requirement and produced to order.
Thread Forms and Tap Types That Can Be Made With a Special Radius
Taylor Tool builds special taps in Acme, trapezoidal, buttress, Whitworth, BSPT, BSPP and PG forms, plus left-hand, multi-lead and large-diameter configurations. If your part calls for an unusual pitch or a form general suppliers don’t stock, the tap can be built for it.
The tap style you pair with the radius depends on the hole and the material:
| Tap type | Best use | Chip behaviour |
|---|---|---|
| Spiral point | Through holes | Pushes chips forward, ahead of the tap |
| Spiral flute | Blind holes, stainless | Pulls chips up and out of the hole |
| Form (thread-forming) | Ductile materials where stronger threads are wanted | No chips; material is displaced, not cut |
| Powdered metal | Heavy machining | Depends on flute design; tough, uniform substrate |
| Carbide | Hardened steels, abrasive materials | Depends on flute design; high wear resistance |
To explore the form-specific options, see special form taps and special Acme taps. For the full range, start at the taps overview. Are special radius taps suitable for blind holes? Yes, with the right style. Spiral flute designs pull chips out of the hole, which is why they’re the usual choice for blind-hole work, while spiral point designs suit through holes.
Choosing Material and Substrate: HSS, Carbide, Powdered Metal
Match the tap substrate to the hardness and abrasiveness of your workpiece. High-speed steel covers general work, while carbide and powdered metal are the upgrades for demanding materials and high volumes.
- HSS: A sound starting point for general-purpose tapping.
- Carbide taps: Carbide offers the wear resistance and rigidity needed for hardened steels, high-silicon aluminum and other abrasive materials, where tool life and consistency drive cost per hole. Yes, special radius taps can be made in carbide; Taylor Tool produces carbide and carbide-tipped taps.
- Powdered metal taps: A uniform, tough substrate suited to heavy machining.
One practical point: grinding a special radius adds complexity to the tap geometry, so substrate choice affects how well the edge holds. Talk through the workpiece material and production volume when you request your quote. If you’re also weighing off-the-shelf performance options, see high performance spiral taps or Quantum taps for comparison.
How to Specify a Special Radius Tap
Send a drawing or a sample, along with the thread form, size, pitch, material and tolerance. Taylor Tool’s engineering team works from either a drawing or a sample to deliver a tap that performs in your application, so a part sample is a valid starting point if no print exists.
When you request a quote, include as much of the following as you can:
- Radius requirement: where it applies (root, crest or form) and the value on your print
- Thread form, size and pitch
- Left-hand or right-hand, and single or multi-lead
- Hole type: blind or through
- Workpiece material and its hardness
- Tolerance and class required on the finished thread
- Volume: one-off prototype or repeat production
- Machine and application notes, such as tapping speed or rigid vs. floating holders
Can a special tap be made from a sample instead of a drawing? Yes, Taylor Tool works from a drawing or a sample. Lead times and pricing depend on your specification, so ask when you quote.
Why Order Special Taps From a Manufacturer
Ordering from a manufacturer rather than a reseller means one party controls quality from design through grinding to delivery. Taylor Tool was established in 1918 and manufactures in Cambridge, Ontario, supplying automotive, aerospace, power generation and general manufacturing customers, from small job shops to large production lines.
For production-critical needs, Taylor Tool offers 24 HR Jet Tap service. In Canada, products are sold through an established distribution network, and the sales team can direct you to your nearest distributor. For U.S. enquiries, call 1-855-221-8277.
Frequently Asked Questions
What is a special radius tap? A special radius tap is a custom tap ground to a non-standard radius on the thread root, crest or form. It’s built to your drawing or sample so the finished thread meets a specific geometry that catalog taps can’t produce.
When do I need a custom radius on a tap? You need one when your print specifies a radius, form or pitch that stock taps can’t deliver. It’s common in fatigue-critical aerospace and power generation threads, and for proprietary thread forms.
How is a special radius tap different from a standard tap? A standard tap follows a published profile and ships from stock. A special radius tap is designed and ground to order around your required radius and thread form.
What information do I need to provide to order one? Provide a drawing or sample, plus thread form, size, pitch, material, tolerance, hole type, hand and volume. See the checklist above.
Can special radius taps be made in carbide? Yes. Taylor Tool produces carbide and carbide-tipped taps for hardened steels, high-silicon aluminum and other abrasive materials.
Which thread forms can be made as special taps? Acme, trapezoidal, buttress, Whitworth, BSPT, BSPP and PG, plus left-hand, multi-lead and large-diameter threads.
Can a special tap be made from a sample instead of a drawing? Yes. The engineering team works from either a drawing or a sample.
Are special radius taps suitable for blind holes? Yes. Spiral flute designs pull chips out of blind holes; spiral point designs suit through holes.
Does Taylor Tool ship custom taps to the United States? Taylor Tool is expanding its U.S. distribution network. Call 1-855-221-8277 for U.S. ordering information.
How do I request a quote for a special tap? Use the contact page, email sales@taylortool.com, or call 1-800-265-2145 in Canada.
Ready to specify your tap? Send your drawing or sample and request a quote, or call 1-800-265-2145 to talk it through with the team.