The sharpest blades. The best quality. A perfect fit between blades, ferrule, and point. NAP is constantly improving Thunderhead components so you can trust Thunderheads on price, quality, and performance - every time. Hardened High Carbon Steel Trophy Tip® cuts on impact. Lock Ring ''O'' Ring Blade Retention System gives perfect head alignment and cushions blades on impact. 0.027'' thick stainless steel blades.  Cutting diameter is 1 1/8" on 75 gr. heads and 1 3/16" on 100 and 125gr.