Description:   The Hornady Lock-N-Load Overall Length Gauge Modified Cases are needed to measure the bullet relationship to the lands of a barrel when being used with the Hornady Lock-N-Load Overall Length Gauge. *Overall Length Gauge Sold Separately.These cases are specially modified to work with Lock-N-Load Precision gauges. A special fine thread is used to attach them to the gauges, ensuring that they remain perfectly square for precise alignment in the chamber of your firearm. Second, the neck of the case is made perfectly round and opened slightly to allow a standard diameter bullet to slip into the case mouth effortlessly, but concentrically, to ensure the most precise results possible.