The tool shown is a vintage L.S. Starrett Co.(Top Tier Manufacturer of Premium Machinist Tools) No. 1 Adjustable Jaw Cut-Nipper (also commonly known as piano wire cutters or music wire nippers).
Design: Features compound leverage and serrated, adjustable/replaceable steel jaws that allow the cutting edges to be repositioned as they are ground down or resharpened. My pics show closeup shots. Minimal rust and masking tape on handles for comfort and ease of use...it is not hiding perfections and can be removed easily.

Application: Traditionally used by piano technicians, machinists, and stringed instrument repairers (for cutting fret wire or music/piano wire).

Condition: The handles in this photo appear to be wrapped in masking or adhesive tape for grip.

Because of their incredible compound leverage and flush-cutting jaw design, Starrett Adjustable Jaw Cut-Nippers are highly prized across several trades.

While they were originally designed for machinists and piano technicians, their unique mechanics make them helpful for a variety of tasks:
Leatherworking & Shoemaking
Leather workers use these nippers primarily for two distinct tasks:
Cutting Heavy Hardware: They easily clip right through thick brass, copper, or steel rivets, snaps, and buckles when adjusting or repairing belts, saddles, and heavy bags.
Vintage Drive-Belt Repair: Historically, machinery and treadle sewing machines were run using round leather drive-belts connected by wire "lacing hooks". These nippers were the perfect tool to close the lacing hooks into the thick leather and snip off the excess wire pins cleanly.
Additional Trade Uses
Beyond leathercraft and piano stringing, you will find these nippers used for:
Lutherie (Stringed Instrument Repair): Guitar builders use them to clip hard nickel or stainless steel fret wire flush against the edge of a wooden fretboard without marring the wood.
Tiling & Mosaics: If equipped with specialized carbide jaws, they provide an adjustable, ultra-powerful bite to snap, nip, and shape hard porcelain, ceramic tile, and glass mosaic pieces.

Jewelry Making & Metalsmithing: Jewelers use them to snip heavy-gauge metal wire, bezel wire, and thick sprues left over from metal casting because the blades cut perfectly flush against a surface.
Bicycle Mechanics: They are a classic choice for cleanly cutting through tough, springy bicycle wheel spokes and thick brake cable housing without crushing or fraying the ends.