The Rockstead RITSU-ZDP Blue is a compact Japanese sheath knife built around ZDP189 clad steel, Honzukuri geometry, a notably thin 3.7 mm blade, a wood micarta handle, and a blue titanium guard. The name RITSU — 律 — suggests rule, measure, and disciplined order. In this model, that meaning becomes physical: a thin Honzukuri blade that moves through material with very low resistance, giving the cut a clean, accelerated quality rather than the heavy feeling of a larger outdoor knife.
  The blade is made from ZDP189 clad by VG10 and hardened to approximately HRc67. The ZDP189 core gives the knife its long-term edge retention, while the VG10 cladding improves corrosion resistance around the core steel. This matters because ZDP189, despite being classified as stainless steel, contains a very high carbon content and may develop small rust spots if exposed to moisture, salts, or an aggressive storage environment.
 The RITSU-ZDP uses Rockstead’s Honzukuri convex geometry in a much thinner format than the larger DON and UN sheath knives. With only 3.7 mm blade thickness, the blade has less material behind the cutting path, reducing resistance as it moves through the target. This gives the RITSU-ZDP a particularly fast, clean cutting character — closer to a precision cutting instrument than to a heavy outdoor fixed knife. The convex bevels are mirror-finished, while the blade’s flat section remains matte, creating a deliberate contrast between optical reflection and restrained surface texture. The absence of distortion in the reflected image is not merely a visual effect; it is evidence of the exceptional accuracy and smoothness of the convex Honzukuri bevels, combined with Rockstead’s extremely fine polishing. 
   The handle is made from wood micarta, giving the knife a stable and practical grip structure. The blue titanium guard creates a precise visual and structural boundary between blade and handle without overcomplicating the construction.
 The RITSU-ZDP Blue is supplied with a dedicated sheath built with a Kydex inner core inside leather. The Kydex core closely follows the shape of the knife, giving the sheath primary friction retention while also creating a more stable and less aggressive storage environment for the polished blade surface. The outer leather gives the sheath a quieter, more traditional presence. The knife is additionally secured by a leather strap closed with a snap fastener. In this construction, retention is not based on a complex mechanical lock: the blade is first held by the fitted Kydex core, then backed up by the leather strap for carry security.
  With an overall length of 213 mm, a 95 mm blade, 3.7 mm blade thickness, and a weight of 123 g, the RITSU-ZDP Blue is smaller, thinner, and more agile than the large DON and UN models. It expresses the Rockstead sheath-knife system in a compact and highly efficient cutting form: ZDP189 clad by VG10, Honzukuri convex geometry, mirror-finished bevels, matte blade flats, wood micarta handle, blue titanium guard, and a leather sheath with a fitted Kydex inner core.
Each Rockstead knife is supplied with an individual passport showing its serial number and actual measured blade hardness, confirming that the hardness value is recorded for the specific knife, not only stated as a general model specification.