Before the ECO: Revision change or Part number change? (2024)

Often, designs go through many iterations from concept through end of life. This post focuses on when to revision change and when to part number change. Oftentimes companies and industries have their own rules, so take the following as a guideline when deciding. ECOs (engineering change orders) arealwaysrecommended for form, fit, or function changes (sometimes finish) and may be required for other changes, depending on your industry.

To rev roll, dash roll, or part number change... that is the question often asked when product change discussions occur. It's not a question to take lightly, as it affects product traceability in the entire system, from your supplier (and sometimes their supplier/s)tothe field. If a recall is later required, changing the wrong level may result in too much product being included in the recall, resulting in good parts being returned. Consideration of why the change is required or desired is also useful - is it something the customer will see or a change to make manufacturing easier, or comply with regulatory requirements, or something else?

A revision roll changes the revision of adrawing. It is typically an alpha or numeric character and may change from numeric to alpha (or alpha to numeric) uponrelease of product from the prototype phase. A dash roll changes the part of the part number after the last hypen in the part - for example, 123-4567-00 might change to 123-4567-01. A part number change changes the entire base part number of the product - for example, 123-4567-04 might change to 123-7654-00.

Parts are generally sold and certified without the part number's dash level to reduce re certification requirements and promote product stability.

When to roll the revision:

• Fixing a typo in the notes that doesn't affect any manufacturing of the parts. For example, "Notes" is spelled "Nots".
• Adding a dimension for clarity on the drawing - when the ruling document is the 3-D CAD model
• Creating a detail view (NO change to dimensions) from a standard view
• Loosening the tolerances on some dimensions (generally to meet as built)
• Removing the revision on a specification and indicating to use "most current revision"
• Updating documents to as-built condition
• Either versioncan be pulled out of a bin containing both of them and placed into the assembly (or sent to the end user)
• Changing from prototype/pilot into production, where production matches the last prototype or pilot version

When to dash roll:

• Minor changes to product that may cause different parts to be used in an upper level assembly, such as modification of a cover that now requires a different length of screw
• Part continues tomate with all custom components without modifying them (or their modification is a dash roll as well)
• Addition/removal of features which affect form or fit but not function (example: adding a clearance feature to resolve an interference)
• If both versions of the part are in a bin, it matters which one is selected
• Parts already in the field are able to be used with this.

When to create an entirely new part number:

• Addition/removal of features which affect function
• It is a brand new product
• The partwillnotwork with all of the otherpartsit used to work with - example could be aconnector that is now longer or shorter, a hinge with more or fewer holes, etc.
• It's a smaller (or larger) version of the otherpart
• It doesn't accept a field-replaceable mating part that field service or a customer would expect it to accept, such as a power supply or cable
• Regulatory requirements (FDA, UL, CSA, etc)

Sometimes an assembly requires a mix of the above -

Example:

A cylinder internal diameter is changed (dash roll), which requires a new spring to be used internally (part number change), but the combination is interchangeable into the top level assembly (revision change). The top level assembly is a revision change because thetop level part with the new spring/cylinder diameteris interchangeable with the the prior revision part containing the old spring/cylinder diameter.

Comments welcome! When else do you rev/dash/part number change?

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