Gauge Number Needle Nominal O.D. (mm) Needle Nominal I.D. (mm) Needle Wall Thickness (mm) Needle Dead Volume (µL/25.4 mm) 34 gauge needle 0.159 0.051 0.051 0.052 µL/25.4 mm 33 gauge needle 0.21 0.108 0.051 0.233 µL/25.4 mm 32 gauge needle 0.235 0.108 0.064 0.233 µL/25.4 mm 31 gauge needle 0.261 0.133 0.064 0.353 µL/25.4 mm 30 gauge needle 0.312 0.159 0.076 0.504 µL/25.4 mm 29 gauge needle 0.337 ..