The Hornady E420 Headspace Bushing is precision-machined to 0.420" specifications for use with the Lock-N-Load Headspace Gauge enabling reloaders to precisely measure cases while sizing them for a perfect fit in any firearm.Hornady E420 - 0.420" Headspace BushingMachined to exacting tolerances for reliable consistent resultsCompatible with bottleneck cases from .17 REM through belted MagnumsWorks with multiple cartridges: 284 WIN 7mm Rem MAG 300 WIN MAG 8mm Rem MAG 338 WIN MAG 375 H&H 7mm STW 7mm Ultra MAG 300 Ultra Mag 300 WSM 338 UltraInterchangeable with all Hornady Headspace Comparator systemsExtends brass life improves accuracy and enhances safetyEssential for serious reloaders seeking precise case measurement and optimal ammunition performance. Requires Hornady Headspace Comparator and calipers (sold separately).