Guide to Threading Metal Pipes for Plumbing Applications

Threading a metal tube is a fundamental job in mechanics. While tapping allows you to create segments for holes or bolts, in this case we are dealing with another metal element: pipes. These structures, widely used in hydraulics, need fittings and joints that often rely on threads that get damaged. Sometimes they are completely missing, preventing the joint.

That's why it's important to understand how to thread pipes, especially those for stainless steel hydraulics that require work performed with precision and quality since they must withstand the pressure of the most insistent substance in nature: water.

What does it mean to thread a metal pipe?

By the term threading we mean the operation necessary to cut grooves into the material in order to create a precise spiral capable of matching with a counterpart. For example, a bolt with a nut or the fitting with the pipe. When we screw a screw into wood we automatically create the modification in the material. Which in this case is soft and adapts to the bolt.

For metal, we must act differently. For example, tapping is the operation necessary to create threads in holes (to explore this further you can read this guide published on Ineco).

The same can be done on the outside to create the thread on bolts and pipes that will be inserted into nuts and other threaded structures with helical coupling.

This image from Wikipedia reminds us that threading consists of a series of elements of extreme precision such as pitch, root, crest and flank.

That's why it's fundamental to proceed with the techniques and appropriate tools to cut the metal with the right proportions. That is, those that allow pipes and fittings or nuts to fit together with the best possible tightening.

What is the purpose of threading hydraulic pipes?

Creating an alternation of external apexes (crests) and internal or roots allows those who work on such activities to create structures useful for completing various types of hydraulic systems. Which can involve a house, an office, a building.

For example, to join two elements or create fittings or joints it is necessary to have pipes ready for use. In many cases already threaded elements are purchased but often joints must be made and pipes shortened, or it's necessary to remake the profile because it's been damaged or stripped. Well, a plumber must always have threads and taps in his workshop to work with metal pipes.

How to thread a hydraulic pipe by hand

First of all you need to secure the iron or steel pipe in a plumber's vise and let a good section protrude so you can work without hitches. Then, choose the right die to create external threading. Insert the nut and start turning with the right tool. The use of oil is very important to facilitate this process. What precautions should you observe?

First, it's advisable to lightly file the contact point between pipe and die to ease the grip. Then you need to turn the tool clockwise to create the thread but after each turn make one counterclockwise to remove metal chips that can damage the tools and ruin the work. This is the process that the die with 5 sharp sides performs.

The tap (which you see above together with a die that cuts the metal profile) takes care of threading the inside of the pipe. The process is similar, only you work with bolts that are screwed into a hole and first do a roughing pass and then must finish the pipe profile always with the same rhythm: one clockwise turn and one counterclockwise. Obviously there are manual techniques but also mechanized processes. That is, you can shape pipes both inside and outside through the use of specific, automated equipment.

What tools are needed to thread

A good pipe working kit you can find in the Krino catalog and includes taps and dies. The former are used to create the internal thread, the latter the external. We have two alternatives: for manual techniques and for manual ones. In both cases there are special requirements in terms of material used. The metal material is always HSS, high speed steel, which guarantees resistance and reliability.

Cobalt models (HSS-CO) are perfect for threading extremely hard materials while the TiN coating ensures extra durability to the tool you use to thread a hydraulic pipe. These tools can vary based on coarse or fine pitch but there are also special tools for very specific uses like hexagonal dies to use with wrenches useful when operating in tight spaces.