The SureFire bore rods are intended for concentricity check prior to firing suppressed on a new platform. The rod most closely represents the bullet flight path and will show any issue of alignment, if present. Recommended to verify barrel to adapter to suppressor alignment, for any new build or any previously unshot setup. Features: Precision machined rods for most accurate verification For validation of set-up prior to first round fired Specific caliber rods for the most popular options on the market today Simply insert rod through the mounted suppressor of an unloaded weapon, equal space should be seen between bore of suppressor and centered rod Made in the USA