The ZJA Series from MMK Matsumoto is a 2-jaw automatic power chuck purpose-built for clamping square bar stock, rectangular cross-sections, and irregularly shaped workpieces on high-precision large-bore lathes. The large through-hole design — a defining feature of the ZJA series — accommodates oversized bar and shaft work while the 2-jaw configuration provides stable, two-point clamping across parallel surfaces.

Why a 2-jaw chuck for square stock?

Square and rectangular bars present two pairs of parallel faces. A 2-jaw chuck grips one pair directly, applying equal and opposite force without the distortion that can occur when a 3-jaw or 4-jaw chuck attempts to distribute clamping across non-parallel surfaces. The ZJA Series jaws are engineered with flat contact faces specifically for this purpose — unlike the V-groove or serrated jaws of general-purpose chucks. The result is full-surface jaw contact across the workpiece face, maximizing friction and minimizing part deformation under high clamping loads.

Size range and selection

MMK Matsumoto offers the ZJA Series in outer diameters from 4 inches (102 mm) up to 18 inches (457 mm), with clamping forces scaling from 31.4 kN at the compact end to 91.2 kN at the largest. Maximum spindle speed ranges from 3,400 rpm (18-inch) to 6,000 rpm (4-inch). The full catalog, including per-size through-hole diameters, dimensional drawings, and mounting interface specifications, is available in the MMK Matsumoto Chucks and Cylinders Catalogue (PDF) on DirectIndustry or from authorized distributors.