Hypodermic needles are available in a wide
variety of outer diameters described by gauge numbers. Smaller gauge numbers indicate larger
outer diameters. Inner diameter depends on both gauge and wall thickness. The following
chart shows nominal inner diameter and wall thickness for regular-wall needles. Thin-wall
needles have identical outer diameters but larger inner diameters for a given gauge.
Needle wire gauge is derived from the Birmingham Wire Gauge. #1=18½ B.W.G.; #2=19 B.W.G.,
and so on to #14=31 B.W.G. See also
French catheter scale chart Stubs Needle Gauge