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  • Dave Nelson thinks this is interesting:

Don’t be tempted to just enter the generic 3mm or 1.75mm, because filament diameter can vary from one manufacturer and even one color to another. Take a digital caliper and measure the thickness of your filament.

From

Cover of Maintaining and Troubleshooting Your 3D Printer

Note

Take as many as 10 measurements along a length of filament and use the average.