The OAL Guages come in both bent and straight versions to suit most action types To use the L-N-L O.A.L. Gauge, you will need to purchase a Modified Case to fit your firearm’s chamber and thread it onto the Gauge. For all bolt action and single-shot firearms, or any firearm with straight-line access to the chamber. This model is preferred, as it is most precise and user friendly. Inserts for each caliber are needed as well as a comparator body. Headspace inserts are also available, see list below:- Designed for use in the Lock-N-Load Headspace Gauge, these bushings are machined to exacting tolerances to ensure reliable results every time you use them. The Lock-N-Load Headspace Gauge allows the reloader to precisely measure cases while sizing them for a perfect fit in any firearm.