NEW BD Ultra-Fine III Mini Pen Needle - 31 gauge x 5 mm (3/16") The world's shortest pen needle - no needle is thinner! Mini Needle requires no pinch-up! Fits all Insulin Pens. The BD Ultra-Fine™ III Mini pen needle is 31 gauge, 5 mm (3/16"). It can be safely used by both children and adults, providing reliable injections with no "pinch-up" of skin required. You should consult with a health care professional before switching to a shorter pen needle.