# Interchangeable Blades for Folding Pocket Tools > A 1987 patent for a folding pocket knife with split handles that can securely swap out different tools, like saw blades, using a locking pivot block and protective aluminum handles. - **Patent:** US 4669140 - **Original title:** Pocket folding tool and knife system - **Owner:** Individual - **Granted:** 1987 - **Status:** Public domain (expired) - **Times cited:** 57 - **Field:** mechanical ## What it does This patent describes a folding multi-tool with two U-shaped handles that swing around to enclose or expose a central blade. It features a mechanism to swap in different tools, such as a saw blade, using a pivoting block with a split (bifurcated) end on one handle. When the handles are closed, a pin on the second handle slides into this split end, locking the interchangeable tool securely in the middle. To prevent the blades from wobbling, built-in centering guides inside each handle hold the tool perfectly aligned. Additionally, the design uses soft aluminum handles with press-fit pivot pins and reinforcing spacers, allowing the user to use the folded tool as a heavy-duty, right-angle screwdriver without scratching or damaging the metal. ## What it does NOT cover - Does not cover multi-tools with single, solid handles where blades fold out like a traditional Swiss Army knife. - Does not cover interchangeable blade systems that do not use a bifurcated pivoting block and mating pin to lock the tool. - Does not cover tools that lack centering guides built inside the U-channel of the handles. - Does not cover folding knives with steel or titanium handles that do not require protective press-fit reinforcing spacers. ## The clever bit Instead of using a complex latch, the tool uses the natural closing action of the two handles to lock the interchangeable blade. The split end of the pivot block on one handle is physically pinned shut by a post on the opposing handle when they meet. ## Real-world examples 1. Modular pocket knives with interchangeable saw and knife blades 2. Early butterfly-style multi-tools 3. Aluminum-handled folding utility knives ## Why it matters This patent represents an early innovation in the consumer multi-tool market of the 1980s, trying to solve the problem of carrying multiple heavy tools. By allowing a single handle system to swap out saws, files, and blades, it paved the way for modern modular pocket tools. It also addressed the manufacturing challenge of using lightweight, cheap aluminum instead of heavy steel for the handles. ## Frequently asked questions ### What does Interchangeable Blades for Folding Pocket Tools cover? A 1987 patent for a folding pocket knife with split handles that can securely swap out different tools, like saw blades, using a locking pivot block and protective aluminum handles. ### Who owns patent US 4669140? Individual owns this patent, granted in 1987. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 4669140 cited by? This patent has been cited by 57 later patents that build on its ideas. ### What problem does this patent solve? This patent represents an early innovation in the consumer multi-tool market of the 1980s, trying to solve the problem of carrying multiple heavy tools. By allowing a single handle system to swap out saws, files, and blades, it paved the way for modern modular pocket tools. It also addressed the manufacturing challenge of using lightweight, cheap aluminum instead of heavy steel for the handles. ### What does this patent NOT cover? Does not cover multi-tools with single, solid handles where blades fold out like a traditional Swiss Army knife. **Full plain-English explainer:** https://patentbrief.org/patent/us/4669140/leatherman-multitool **Original patent:** https://patents.google.com/patent/US4669140 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Modern Rollerblades Became Adjustable and Interchangeable](https://patentbrief.org/patent/us/4492385/inline-skates-rollerblade-olson) — A 1982 patent describing a skate design that allows users to swap between wheels and blades and adjust their position on the boot for better performance. - [How Jacob Schick Invented the Modern Magazine-Loading Safety Razor](https://patentbrief.org/patent/us/1721530/schick-repeating-razor) — A 1929 patent for a safety razor that uses a replaceable blade magazine, allowing users to change blades without touching the sharp edges. - [How King Gillette Invented the Modern Disposable Safety Razor](https://patentbrief.org/patent/us/775134/safety-razor-gillette) — King Gillette's 1904 patent for a safety razor with a thin, replaceable, double-edged blade that changed how the world shaves. - [How the String Trimmer (Weed Eater) Actually Cuts Grass](https://patentbrief.org/patent/us/3826068/weed-eater-string-trimmer) — This 1974 patent describes the mechanics of using a high-speed spinning plastic line to cut grass, replacing dangerous metal blades with flexible, non-metallic material. - [How Joshua Pusey Invented the Paper Matchbook](https://patentbrief.org/patent/us/483166/matchbook-pusey) — A 1892 patent for a method of creating a booklet of paper matches where the striking surface is tucked inside to prevent accidental fires.