The specifications of common LED tube are T8, T5, T4 tube, a group of three tubes used by companies is usually T5 tube, the specifications of LED tube commonly used were T10, T12 a long time ago.
“T”, on behalf of “Tube”, indicates tubular, the figure behind T is the tube diameter. T8 is to have eight “T”, a “T” is 1/8 inch.
One inch equals 25.4 mm. Then every “T” is 25.4 ÷ 8 = 3.175mm