Method guide · Root cause analysis and problem solving
The 6 Ms of production (the 6M method)
Short answer
The 6 Ms are Man, Machine, Method, Material, Measurement and Mother Nature (the environment). They are the six cause categories of a fishbone, or Ishikawa, diagram. A team takes one clearly stated problem and lists the possible causes under each M so no area gets skipped. Listing a cause doesn't prove it, so the team checks the likely ones against evidence before it acts.
The six Ms at a glance
The table shows what each M covers and a first question to ask about it. Our complete guide to the 6 Ms goes through every M in depth, with a longer list of questions for each.
| M | Also called | What it covers | A first question to ask |
|---|---|---|---|
| Man | People, manpower | Skills and training, staffing, fatigue, shift handover, role clarity | Was the person trained for this job, and what made the error easy to make? |
| Machine | Equipment | Condition and maintenance history, capability for the tolerance, tool wear, settings, controls | When was it last maintained, and what has changed since the last good run? |
| Method | Process, procedure | Written procedures, informal workarounds, process design, consistency between shifts | Is there a current procedure, and is it what people actually do? |
| Material | Inputs | Supplier and lot changes, specifications, incoming inspection, storage and handling | Did the supplier, grade or lot change? |
| Measurement | Inspection | Gauge capability and calibration, repeatability, sampling plans, how data is recorded | Can the gauge reliably tell good parts from bad ones for this characteristic? |
| Mother Nature | Environment, milieu | Temperature, humidity, vibration, lighting, air quality, seasonal change | Does it happen more at certain times, in certain seasons or in one part of the plant? |
Two Ms get skipped more than the others. Mother Nature, because teams rarely think about the environment unless the pattern is obvious, and Measurement, because a defect that was caught makes the gauge look fine. Give both their own time in the session.
How to run a 6M session
- 1
Write one problem statement
Say what, where, when and how much, for example "Bore diameter out of tolerance on CNC 4, afternoon shift, 14% of parts over three weeks". "Quality issues on the machining line" gives the team nothing to test. The 5W1H template helps you pin it down.
- 2
Draw the six bones
Put the problem at the head of a fishbone and give each M its own bone, on a whiteboard or on the printable fishbone template.
- 3
Take the Ms one at a time
Collect causes for one M before moving to the next, so the discussion doesn't pile up on Machine or whichever bone the team already suspects. Every M gets time, including the ones people are sure don't apply.
- 4
Keep Man about the system
When someone writes "operator error", ask what made the error possible: an unclear procedure, missing training, staffing pressure or a handover that left something out.
- 5
Ask why on the causes that matter
Take each likely cause through the 5 Whys until you reach a condition you can change for good.
- 6
Check before you act
Mark which causes have evidence behind them and which are guesses, then go and look, pull the data or run a test. Check a condition that shows up on several bones first.
- 7
A short example
This example is illustrative, not from a real plant. Paint on a steel bracket has failed the adhesion test on about one part in twenty for the last four weeks, mostly on the night shift. The team listed one candidate cause per M and a way to check each one.
| M | Possible cause | How to check it |
|---|---|---|
| Man | A new night-shift sprayer not yet signed off on pre-treatment | Training records for the shift |
| Machine | Spray gun pressure drifting between setups | Pressure readings per shift |
| Method | Flash-off time cut short to keep up with output | Watch the line and compare with the procedure |
| Material | A new lot of primer from a second supplier | Lot numbers on the failed parts |
| Measurement | Inspectors run the adhesion test in different ways | Two inspectors test the same parts |
| Mother Nature | Colder, damper air at night near the loading door | Temperature and humidity log by hour |
Illustrative, not a benchmark.
Without the Measurement and Mother Nature bones, nobody would have written down the last two causes, and the argument would have stayed on the sprayer and the gun.
5M, 6M and other versions
Kaoru Ishikawa's cause-and-effect diagram, from the 1960s, used five categories: Man, Machine, Method, Material and Measurement. Mother Nature was added later, when plants kept finding defects that followed temperature, humidity or vibration and fitted none of the five. Use all six when the process is sensitive to its surroundings or the problem follows a time, a season or a place. Five can be enough in a stable, controlled room. The 5Ms guide covers the five-category version.
Other fields rename the bones. Healthcare teams sometimes call the sixth M Milieu, and marketing teams use Market, Message, Media, Money, Management and Measurement. In general management, "the 6 Ms" can also mean men, money, materials, machinery, methods and markets, which is a list of business resources, not cause categories.
Where the 6 Ms fit in problem solving
- Before the fishbone, define the problem with 5W1H or an is/is not analysis.
- During it, the 6 Ms give the fishbone diagram its bones and the 5 Whys take each likely cause deeper.
- After it, verified causes go into the cause section of an A3 or the root-cause step of an 8D, and into corrective action if it was a quality failure.
- When the cause sits under Measurement, a measurement system analysis shows whether the gauge can be trusted.
Go deeper
This page is the short version. These guides cover each part in full.
- The 6Ms of Production: A Complete Manufacturing GuideThe full guide: where the framework came from, each M in depth with investigation questions, and how the Ms show up in quality, equipment, yield and safety problems.
- The 5Ms of Lean Manufacturing: How Fishbone Diagram Categorizes CausesThe original five categories and when the sixth M is worth adding.
- Fishbone Diagram: A Root Cause Analysis Visual ToolHow to build the diagram step by step, with a manufacturing example.
- Fishbone Diagrams: Effective Facilitation Techniques for Manufacturing TeamsPreparing and running the session, the usual facilitation mistakes, and turning findings into action.
- What is the 5 Whys Root Cause Analysis Method?Taking one cause from symptom to root, and when another tool fits better.
- Top Root Cause Analysis Tools for Manufacturing Problem SolvingWhich tool fits which kind of problem: 5 Whys, fishbone, FMEA, Pareto, fault tree and A3.
All our articles on this subject are in the root cause analysis and problem solving topic.
Free templates and tools
- Fishbone diagram template (6M)A printable six-M fishbone on one landscape sheet, plus the fishbone board in Lean Studio: problem statement at the head, a bone for each M and a table for the causes you will check.
- 5W1H templateSix questions with prompts and evidence, turned into a problem statement before the root cause analysis.
- 5 Whys templateA problem statement, five why rows with evidence, the root cause and the countermeasure.
- A3 problem solving templateThe standard seven-box A3 on one landscape sheet, from background to follow-up.
- 8D report templateD0 to D8 on three pages: team, is/is not, containment, occurrence and escape causes, actions and closure.
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