Raceworks Rubber hose. Sizes range from -4 to -20 and in various pre-cut lengths. Rubber hose is for use with raceworks or other brand rubber hose ends, or with basic hose barbs. Sizing is as follows : -4 = 1/4" ID, -5 = 5/16" ID, -6 = 3/8" ID, -8 = 1/2" ID, -10 = 5/8" ID, -12 = 3/4" ID.