The Short Heavy Duty needle has an effective length of 0.5". The effective length of the needle is the portion of the needle that extends past the end of the tagging gun.
Heavy Duty needles have a larger diameter than standard needles. The larger diameter makes them better able to stand up to the wear and tear of tougher materials such as canvas or leather. The larger diameter also enables you to use heavy duty fasteners which have a higher tensile strength than regular fasteners.