Harness needles size 3 are used for saddle stitching leather with an awl to pierce the holes. These needles blunt points prevent piercing the thread as it goes through the hole.
#1 is heaviest and best for holsters, saddles, etc., while #6 is best for fine work like lightweight bindings. For general, #3 is a good size.
Size #3, 20 Gauge, 2-1/4", Package 5
See related items below for other sizes.