sˌiːtˌiːˈɛs daɪˈæmɪɾɚɹ ˈɔːlweɪz spˈɛsᵻfˌaɪz ðɪ aʊtsˈaɪd daɪˈæmɪɾɚ ˌoʊdˈiː əvə tˈuːb, wˌɛɹ pˈaɪp daɪˈæmɪɾɚ spˌɛsɪfɪkˈeɪʃənz ˈoʊnli ɐpɹˈɑːksɪmət ðə pˈaɪp ɪnsˈaɪd daɪˈæmɪɾɚ aɪdˈiː fɔːɹ sˈaɪzᵻz ʌv twˈɛlv ˈɪntʃ ɔːɹ lˈɛs, ænd ˌɛstˌiːdˈiː wˈɔːl θˈɪknəs.
CTS diameter always specifies the outside diameter (OD) of a tube, where pipe diameter specifications only approximate the pipe inside diameter (ID) for sizes of 12 inch or less, and STD wall thickness.