Turning Tools: The Ins & Outs


Published: 10/03/2022

What Is CNC Turning?

CNC Turning is a manufacturing process in which bars of material are held in a chuck and rotated while a tool is fed to the piece to remove material to create the desired shape. There are many different kinds of CNC turning centres with various types of tooling options, spindle options, outer diameter limitations as well as power and speed capabilities that affect the types of parts that can be economically made on it. There are tiny & mini turning tools, ISO Lathe Tools, Live Centres & more variations of turning tools. Today, we will be identifying ISO lathe tools. The holders, the inserts, and everything in between.

To break it up, we will make our way through learning the Turning Tool ISO Code System.

All boring bars & turning tool holders codes are made up of random letters & numbers. However, these letters & numbers are not actually random. Each individual character defines a different part of the tool. 

Below is an example:

clamping method of inserts

1. Clamping Method Of Inserts

There are 5 different clamping methods on turning tools, as shown. Each clamping method has different capabilities, pro's and cons. Let's discuss these.

C Clamp Style - Top Clamping Without Hole

D Clamp Style - Top & Hole Clamping (Multi Clamp, Pin & Clamp)

M Clamp Style - Top & Hole Clamping (Multi Clamp, Pin & Clamp)

P Clamp Style - Hole Clamping (Pin Lock)

S Clamp Style - Screw On

turning insert shape

2. Insert Shape

Number 2 is the part of the ISO Code which adheres to the shape of the insert. It can sometimes be as simple as S = Square & T = Triangle, but as we know, life isn't always this easy. You have C, D, E, K, R, S, T, V & W shape inserts.

C Shape Insert - I like to remember this one as 'Crushed Square' - It is ultimately a slanted square shape with a 80 degree angle.

D Shape Insert - I like to remember this one as 'Diamond' - It has a 55 degree angle.

E Shape Insert - This shape has a 75 degree angle.

K Shape Insert - The K shape insert has the same 55 degree angle as the D shape, however it is more rectangular than square.

R Shape Insert - R is simple and stands for a round insert.

S Shape Insert - S stands for Square.

T Shape Insert - T stands for Triangle and has a 35 degree angle.

V Shape Insert - The V shape insert has a 55 degree angle.

W Shape Insert - The W shape insert has an 85 degree angle.

turning holder style

3. Holder Style

The third part of the iso code is to select the style of turning tool. It primarily affects the angle of the holder. 

A - 90 degree holder                            K - 75 degree holder

B - 75 degree holder                            L - 95 degree holder

C - 90 degree holder                            N - 63 degree holder

D - 45 degree holder                           Q - 117 degree holder 30'

E - 60 degree holder                            R - 75 degree holder

F - 90 degree holder                            S - 45 degree holder

G - 90 degree holder                           T - 60 degree holder

H - 107 degree holder 30'                  V - 72 degree holder 30'

J - 93 degree holder                            X - 113 degree holder

Z - 100 degree holder

clearance angle of inserts

4. Clearance Angle Of Inserts

Positive Turning Insert ( B, C & P )

A positive insert has an angle of less than 90° (7° clearance angle).

  • Single sided
  • Low cutting forces
  • Side clearance
  • First choice for internal turning and for external turning of slender components

Negative Turning Insert ( N )

A negative insert has an angle of 90° (0° clearance angle).

  • Double and/or single sided
  • High edge strength
  • Zero clearance
  • First choice for external turning
  • Heavy cutting conditions
hand of tool

5. Hand Of Tool

The hand of tool is simple. R is a right handed holder. L is a left handed holder & N is a neutral holder. This then corresponds with what insert you put in.

height of shank

6. Height Of Shank

Boring bars are round and have no sides, but turning tool holders have 4 sides. The height of these sides can be determined on the 6th part of the ISO code. For this example, '25' would mean the height of the shank is 25mm.

width of shank

7. Width Of Shank

Following from point 6, the 7th part of the ISO determines the width of the shank. Again, for this example, '25' would mean the width of the shank would be 25mm.

length of holder

8. Length Of Holder

The 8th part of the ISO code corresponds to the overall length of the holder. This is determined by a letter. In this example, 'M' would be 150mm in length. This part of the code is important to know, especially if the holder you want is unavailable. If you know the length, then it is easier to find an alternative.

length of insert cutting edge

9. Length Of Insert Cutting Edge

The 9th and final part of the ISO code, corresponds to the length of the inserts cutting edge. In this example, '12' would mean the insert cutting edge is 12mm. We can use this to find the insert we would need to fit in the holder. The last part of the ISO code corresponds with the first numbers in the inserts code. 

Using the ISO Code, you can find the holder you need, but also the inserts to go with it.


By Using 1 (clamping method) , 3 (holder style) , 5 (hand of tool) , 6 (height of shank), 7 (width of shank)  & 8 (length of holder) - you can find the exact turning holder you need.

Using 2 (Insert Shape) , 4 (Clearance angle of insert) & 9 (length of insert cutting edge) - you can find the insert you need for the holder.


In this example, the holder is PCLNR 2525 M12 - so the insert would be CNMG12****


In terms of clamping method, and other options to choose from, there is no right or wrong answer. It all comes down to the application you are using, and the operators personal preferences. 

turning 1
turning 2
turning 3