Multiple sources have confirmed that Kai U.S.A. LTD., maker of Kershaw, Zero Tolerance, and Shun knives, has taken action to defend its 2015 U.S. sub-framelock Patent.

Sources say that Kai U.S.A. LTD. sent Microtech a Cease and Desist letter prior to June 3rd. Microtech planned to bring sub-framelock knives to Blade Show, but these knives were noticeably absent from the event. Popular Microtech folders and Marfione custom versions, including the D.O.C., the Whale Shark, and the Socom Delta, use sub-framelocks. In addition to the letter to Microtech, dealers received an email requesting that they begin phasing out Microtech models infringing on the Patent, and stop selling them by August 1st.

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Knives from other manufacturers appear to utilize locks similar to a sub-framelock construction. Several of these makers told us they haven’t received communication from Kai U.S.A. LTD. regarding the matter, but it is still unclear if Microtech is the only manufacturer currently affected.

U.S. Patent no. 9,120,234 describes a sub-framelock: “the lockbar and the handle are separate pieces. The handle includes a pocket into which at least a portion of the lockbar is fit.”

Kai U.S.A. LTD. debuted the sub-framelock on the famous Zero Tolerance 0777. The upcoming Limited Edition ZT0427 appears to use an inset lock as well, although it is not described as a sub-framelock on the Zero Tolerance website. The Kershaw Knockout is the only sub-framelock knife Kai U.S.A. LTD. currently sells.

Knife featured in image: Microtech Marfione Custom Socom Bravo Carbon Fiber High Polish Tanto