In simple terms and usages, the word dimension means a measurement of the size of something in a particular direction, such as the length, width, height, or diameter. Examples of the units of measurement include: - Imperial System... inches, feet, yards, miles, etc - Metric system...... centimeters, meters, kilometers, etc. The word "size' is used to compare the amount of space that an item takes, usually does not include units of measurement, and is most often described by an adjective such as: - small - medium - large - tall - short, or - a number used to describe the size of an article, such as, shoe size, clothing, etc. So, in your example, the word dimension must be used because you 'measured the item and reported the dimensions'.

"I measured some of the dimensions of these two parts and all the dimensions are the same." Size means how big the part is overall. Size would make sense if by "part" you actually mean type/brand/class of part, and they come in various sizes, and you want to make sure all the sizes match each other. I do not think that is what is meant, though.