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. For use with the Hornady Headspace Comparator Provides the ability to check most bottleneck cases from .17 REM through belted Magnums (See description for models that apply to this size) Extend brass life improve accuracy and enhance safety All bushing are interchangeable with the Comparator Bullet comparator and calipers sold separately E-.420" 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 Ultra