Double Ball Screw

A double ball screw, more accurately called a double nut ball screw, uses two coordinated ball nuts on one screw shaft. Preload between the two nuts reduces axial clearance and increases axial rigidity, helping the transmission maintain stable positioning when the travel direction changes repeatedly.

DLY supplies both DFU and DFI double nut ball screw series. DFU follows a DIN-style flange configuration, while DFI uses a different flange and mounting geometry. The appropriate series should therefore be selected according to the machine mounting space, flange dimensions, screw diameter, lead, load and required stiffness-not by model name alone.

Standard production uses a rolled C7 screw shaft made from S55C and a 20CrMo ball nut. Ground C5 versions, custom shaft length, left-hand thread, end machining and matching support units can be supplied after technical confirmation.

DLY double nut ball screw and screw shaft assembly

Structure and Preload

Each nut contains its own ball circulation path. During operation, the balls roll between the screw raceway and nut raceway, converting rotary motion into controlled linear movement.

The two nuts are assembled with a controlled preload. The preload creates opposing axial forces that reduce clearance between the balls and raceways. Compared with a standard-clearance single nut, this structure provides better axial rigidity and more stable reversal performance.

"Zero backlash" should be understood as a preload objective rather than an unconditional value for every installed system. Actual positioning performance is also affected by screw accuracy, support-bearing clearance, coupling stiffness, mounting alignment, temperature and machine structure.

DFU and DFI Series

DFU and DFI belong to the same double nut ball screw category, but they are not automatically interchangeable. Before replacing an existing unit, compare the nut outside diameter, flange outside diameter, flange thickness, overall nut length, flange width, mounting-hole position and mounting thread.

DFU Dimensions

DFU double nut ball screw structure and dimension symbols

Dimensions are in mm. Ca and Coa are shown in kgf; K is shown in kgf/μm. Final dimensions and ratings should be confirmed against the approved drawing before ordering.

DFI Dimensions

The DFI series is also a flanged double nut ball screw, but its nut outside diameter, flange size and mounting dimensions differ from the DFU series. The table below should be used together with the approved DFI dimension drawing.

* Models marked with an asterisk are identified as custom nut specifications in the supplied DFI data. Dimensions are in mm. Ca and Coa are in kgf; K is in kgf/μm. Values such as "30/28" indicate alternative outside-diameter data in the source table and require drawing confirmation.

Model Code

In DFU1605-4 and DFI1605-4, the model code indicates the nut series, nominal screw diameter, lead and circulation configuration:

Accuracy and Materials

End Machining and Support Units

Shaft ends can be machined according to the customer's drawing or confirmed support-unit dimensions. Available operations include bearing seats, retaining threads, locknut threads, coupling seats, keyways, wrench flats and center holes.

Depending on the screw diameter and machine arrangement, the assembly can be matched with BK/BF, FK/FF or EK/EF support units. End dimensions must be checked together with the fixed-side bearing arrangement, motor coupling and available installation space.

Applications

Selection Checklist

FAQ