Each color needle is a different size gauge. This is to allow the use of different viscosities of cutting oils. We offer the following oil needles: Part Num. Color Gauge 31-5001-9002 Clear .2mm 31-5001-9003 Red .25mm 31-5001-9004 Orange .33mm 31-5001-9005 Blue .41mm 31-5001-9006 …