1/4" female insulated. Blue; for 16-14 gauge (1.0 to 2.5mmý or 1.02mm to 1.63mm diameter) wiring. Crimp connectors with the extra insurance of heat shrink tubing. Stronger than just a crimp. Offers improved durability; vibration and weather resistance. Note: See 951779 for the matching male Slide-On connector.