Description
Details
DFU Double Ball Screw Nut — Anti-Backlash Preloaded Nut for Precision Ball Screws
| Model | Specification of Ball Screw Shaft and Nut | |||||||||||||||
| d | l | Da | D | A | B | L | w | X | H | Q | n | Ca | Coa | K | SKU | |
| DFNUR1605-4 | 16 | 5 | 3.175 | 28 | 48 | 10 | 96 | 38 | 5.5 | 40 | M6 | 4 | 1380 | 3052 | 32 | 1035101 |
| DFNUR2005-4 | 20 | 5 | 3.175 | 36 | 58 | 10 | 101 | 47 | 6.6 | 44 | M6 | 4 | 1551 | 3875 | 39 | 1035102 |
| DFNUR2505-4 | 25 | 5 | 3.175 | 40 | 62 | 10 | 101 | 51 | 6.6 | 48 | M6 | 4 | 1724 | 4904 | 45 | 1035103 |
| DFNUR2510-4 | 25 | 10 | 4.762 | 40 | 62 | 12 | 145 | 51 | 6.6 | 48 | M6 | 4 | 2954 | 7295 | 50 | 1035104 |
| All product data (pictures, dimensions, tables, drawings) are provided as received from the supplier; we exclude liability for their accuracy or completeness. | ||||||||||||||||
Symbols used in the table: d = shaft diameter, l = lead, Da = ball diameter, D = nut outer diameter, A = flange diameter, B = flange thickness, L = total nut length, w = flange bolt circle, X = flange hole diameter, H = flange hole spacing, Q = grease nipple thread, n = number of ball circuits, Ca = basic dynamic load rating (kgf), Coa = basic static load rating (kgf), K = rigidity (kgf/μm).
Double Nut, Preloaded, Zero-Backlash Design
The DFU Double Ball Screw Nut is an anti-backlash double-nut assembly designed to be mounted on rolled or ground ball screw shafts of matching diameter and lead. The double-nut construction uses two recirculating ball nuts preloaded against each other through a calibrated spacer, eliminating axial play between the nut and the screw shaft. This makes the DFU series suitable for CNC routers, milling machines, engraving systems, 3D printers, and any motion axis where positioning repeatability is critical.
Key Features:
- Double-Nut Anti-Backlash Construction:
Two ball nuts are preloaded against each other through an internal spacer, removing axial clearance and giving repeatable bidirectional positioning. - Recirculating Ball Bearing Path:
Hardened steel balls circulate through internal return channels, converting rotary motion of the screw into linear motion of the nut with low friction. - Flange-Mounted Body:
The cylindrical nut body terminates in a mounting flange with through-holes for direct bolting to a carriage or machine bracket. - Compatible with Standard Ball Screw Shafts:
Each variant matches a specific shaft diameter and lead combination (16, 20, or 25 mm shaft with 5 or 10 mm lead). - CNC and Industrial Use:
Suitable for X, Y, and Z linear axes in CNC machines, automation equipment, and motion stages.
Applications:
The DFU double nut is used on CNC routers, mini mills, engraving machines, gantry systems, and industrial linear stages where backlash-free travel is required. It pairs with a matching SFU/DFU-class ball screw shaft of the same nominal diameter and lead.
Ball Screw & Stepper Motor Calculator
Use the calculator to match ball screw lead and speed with stepper motor torque, current, voltage and step resolution for your CNC axis.
Preload / Backlash Adjustment
Preload on a DFU double-nut assembly is set by changing the relative axial position of the two nuts against the precision spacer that sits between them. The two nut bodies are clamped together through the flange couplings using a set of axial screws. By tightening or loosening these screws in a controlled, gradual sequence, one nut is finely advanced toward or backed away from the other, which compresses or releases the ball trains against opposite flanks of the screw thread.
The practical procedure is:
- Mount the assembly on the ball screw shaft and keep the shaft fixed.
- Loosen the flange clamping screws so the two nuts are free of preload.
- Tighten the screws progressively and evenly in a cross pattern, in small increments.
- After each increment, rotate the nut by hand on the shaft and judge the resistance to rotation by feel — the torque should be smooth, uniform along the stroke, and free of stick-slip.
- Continue until the desired rotational drag is reached, then secure the screws to their final torque.
Whether a higher or lower preload is preferable depends on the application. A higher preload removes more backlash and increases axial and torsional stiffness, which benefits positioning accuracy and rigidity in machining; the trade-offs are higher driving torque, more heat, and reduced service life. A lower preload gives lower friction, less heat, and longer life, at the cost of slightly more compliance under reversing loads. For general positioning duty a light preload is typical; for high-stiffness machining axes a medium preload is more common. Avoid overtightening — excessive preload can damage the ball tracks and shorten the screw life significantly.
Reliability & User Benefits
- Backlash elimination: The double-nut preload removes axial play, improving bidirectional positioning repeatability on CNC axes.
- Higher rigidity: Preloaded double nuts deflect less under reversing loads compared with a single non-preloaded nut.
- Low friction motion: Recirculating ball contact gives a high mechanical efficiency compared with sliding lead screws.
- Standard mounting interface: The flange pattern matches the common DFU footprint used in CNC kit builds and industrial replacement scenarios.
- Maintenance access: The grease port allows periodic relubrication of the ball circuits to extend service life.
FAQ frequently asked questions
Will this nut work on any 16, 20, or 25 mm ball screw?
The nut must match the shaft of the exact same nominal diameter and the same lead. A DFNUR1605-4 fits a 16 mm shaft with 5 mm lead only — it is not interchangeable with a 16 mm shaft of 10 mm lead.
Are DFU and SFU nuts interchangeable?
Yes. DFU (double) and SFU (single) nuts of the same nominal diameter and lead share the same flange and outer housing interface — the only dimensional difference is the overall nut length. This means both types fit the same DSG nut housings and brackets, so a DFU can be swapped in place of an SFU (or vice versa) without changing the mounting hardware.
What is the difference between a single nut and a double nut?
A single nut has one set of ball circuits and typically has a small amount of axial backlash. A double nut uses two nut bodies preloaded against each other through a spacer, which eliminates that axial play.
Does it require lubrication?
Yes. Ball screw nuts require periodic greasing through the grease port to maintain low friction and extend ball and raceway life. Follow the lubrication interval recommended in the manufacturer manual.
Can the preload be adjusted by the user?
Yes. The preload is defined by the spacer thickness between the two nut bodies, so an experienced end user can change it by swapping the spacer for one of a different thickness. Do not disassemble the nut off the shaft during this operation, or the balls will fall out of the circuits — use a transfer arbor of the correct diameter to keep the ball circuits loaded.
