Taps vs Hex Dies: Which Threading Tool Do You Need?
By Products for bench top machinists | LittleMachineShop.com | Published: 2026-11-04
Category: Comparisons
Compare plug taps and hex dies for internal and external threading. Learn which tool suits your bench machining job and the trade-offs of each.
Quick answer
Use a tap for internal threads and a die for external threads. For most bench machining, a plug-style tap handles through or blind holes, while a hex die is the practical choice for rethreading or cutting external threads with a wrench or socket.
Internal vs external threading: the basic split
The tap and die difference comes down to where the thread lives. A tap cuts threads inside a hole, such as a nut or a tapped block. A die cuts threads on the outside of a rod or screw blank. Bench machinists often need both, but rarely for the same operation.
If you are threading a hole, you need a tap. If you are threading a shaft, you need a die. Buying the wrong one is the most common mistake when starting out.
Plug style tap uses and limitations
Plug taps have 3-5 chamfered threads, which makes them suitable for both through and blind hole tapping. They are the general-purpose choice for free machining steels, stainless steels, aluminum, zinc, and ductile materials.
The trade-off is that plug taps are not designed for bottoming holes where threads must run very close to the bottom. For that, a bottoming tap is needed. Also, hand tapping requires careful alignment to avoid breaking small taps.
Hex die vs round die: what matters for external threads
A hex die has a hexagonal outside shape that fits a standard wrench or socket (19/32 or 15mm). That makes it convenient for rethreading damaged bolts or cutting threads in tight spots with hand tools. Round dies typically need a die stock or holder and offer more adjustment for thread fit.
The hex die is carbon steel in the supplied record, which suits general external threading but may wear faster than high-speed steel in production work. If you need precise thread diameter control, a round die with adjustment is often preferred.
Key trade-offs
- Internal vs external threading: Taps cut internal threads; dies cut external threads. Choose based on whether the thread is inside a hole or on the outside of a part.
- Plug tap hole compatibility: Plug taps handle both through and blind holes, but they are not ideal for bottoming holes where threads must reach the bottom. For bottoming holes, use a bottoming tap instead.
- Hex die convenience vs round die control: Hex dies fit a wrench or socket for quick rethreading, while round dies typically need a die stock and allow more adjustment for thread fit. If you need precise thread diameter, consider a round die with adjustment.
Product facts
- Taps, Plug Style, Individual Sizes: Plug style taps with 3-5 chamfered threads, sold individually in UTS sizes. These taps work for both through and blind holes, giving you flexibility for general bench machining tasks.
Taps, Plug Style, Individual Sizes - Dies, Hex, Individual Sizes: Hex rethreading die made of carbon steel, right-hand style, fits a 19/32 or 15mm wrench or socket. This die is handy for repairing external threads quickly with common hand tools, without a separate die stock.
Dies, Hex, Individual Sizes
Which should you choose?
Best for
- Cutting internal threads in through or blind holes with a plug tap
- Rethreading external threads with a hex die and a standard wrench or socket
Not for
- Bottoming holes that require threads to the bottom (use a bottoming tap)
- High-precision external threading where thread diameter must be adjusted (use a round die with die stock)
