What is the importance of O.D. and I.D.?

Failure to adhere to diameter tolerances can produce a diversity of undesirable performance characteristics in NMR spectroscopy. If the I.D. is too large, coaxial inserts can move during spectral accumulation. If the I.D. is too small, any insert can burst the tube making sample loss a catastrophic possibility. If the O.D. is too small, the tube might slip in the spinner turbine. This can cause the tube to become unsteady and cause modulation sidebands. If the O.D. is too large, the tube may not fit in the spinner turbine. Also, the tube can come in contact with the inner surfaces of the probe causing damage and costly repairs.  more