Antique Dahl Mfg Co Interlox Master Slide Rule 48\" Wood Ext Ruler NYC Approved For Sale

• Item Name: Antique Dahl Mfg. Co. \"Interlox\" Master Slide Rule (48-Inch / 4-Foot Wood Extension Rule)

• Manufacturer: Dahl Manufacturing Company (New York City, NY, USA)

• Estimated Era: c. 1910 – 1918

• Historical Significance: This is a fantastic pre-1919 tool. In 1919, Dahl Mfg. Co. transitioned into the well-known Master Rule Manufacturing Company. Because this piece still bears the original Dahl Mfg. Co. branding, it is a highly prized early variant for antique tool purists.

Up for consideration is a rare and mechanically ingenious piece of early 20th-century American craftsmanship: an antique Dahl Mfg. Co. \"Interlox\" Master Slide Rule.

Unlike the more ubiquitous zig-zag folding rulers that took over the market in the 1920s, this specialized slide rule utilizes a series of parallel boxwood sections that slide smoothly past one another via an intricate system of interlocking brass spring guides. This design allowed woodworkers, shipbuilders, and masons to quickly expand the tool and lock it into place, then smartly collapse it in a single fluid motion.

• \"MASTER SLIDE RULE\" — Stamped inside the section profile, highlighting the original patented design by Hermann Gasstrom.

• \"DAHL MFG. CO. / N.Y.C.\" — Explicitly labels this piece as an early pre-1919 production run before the company reorganized into the Master Rule Mfg. Co.

• \"N.Y.C. APPRD X-4\" — A highly desirable New York City Department of Weights and Measures official inspector approval stamp, certifying the rule\'s strict precision for commercial trade use.

As verified in the detailed layout photos, this rule measures roughly 8 inches when fully closed but telescopes cleanly out to a maximum length of 48 inches (4 feet), culminating in a beautiful protective flush brass end-cap. The dual-sided markings accommodate both standardized outside measurements and specialized inside dimensions. Whether you are a dedicated collector of New York industrial history, a lover of fine antique jointer and carpentry tools, or looking for an incredibly unique functional display piece, this Dahl extension rule is an exceptional survivor.

• Closed Length: Approx. 8 inches

• Extended Length: 48 inches (4 Feet)

• Materials: Boxwood body segments with premium warded brass locking guides

• Origin: Made in New York City, USA

• NYC Inspection Mark: As showcased in image verbatim file name 20260626_151930.jpg, the \"N.Y.C. APPRD\" stamp is a major selling point. Tool collectors heavily value regional weights-and-measures validation marks because it links the physical tool to authentic early municipal regulatory history.

• The Number \"5\" Stamping: Photographed close-up in image verbatim file name 20260626_151840.jpg and 20260626_151926.jpg is a prominent numeral \"5\" next to the factory name. This may indicate a specific early series or model pattern before they standardized their numbering scheme to the 100-series (e.g., 104, 106).

• Excellent Spring Action: The core image verbatim file name 20260626_152146.jpg illustrates the internal brass tension clip. The fact that all pins catch and the assembly slides smoothly as a complete mechanism prevents value-drop from loose or detached wood tiers.

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