Armstrong 19-937 3/8-Inch Drive Impact Locking Extension, 12-Inch Made in the USA - quality and availability Incorporates a pin on the square drive providing maximum security against accidental disengagement of the socket, safety Socket is securely locked to the extension and will not disengage until knurled sleeve is pulled, safety and convenience Manufactured from high alloy steel using the most up-to-date manufacturing process and heat treat for greater strength and durability