When customers ask for the "pitch of a ball screw nut," they usually mean the lead of the matching ball screw: the axial distance that the nut travels during one complete revolution.
For example, an SFU1605 ball screw has a nominal diameter of 16 mm and a lead of 5 mm. One revolution moves the nut approximately 5 mm along the screw. However, pitch and lead are not always identical, so the two terms should be distinguished when confirming a model or preparing a drawing.
Does a Ball Screw Nut Have Its Own Pitch?
A ball screw nut does not normally have an independently selectable pitch. Its internal helical raceway must match the screw shaft's:
- Nominal diameter;
- Lead and thread pitch;
- Thread direction;
- Number of thread starts, where applicable;
- Ball diameter and raceway geometry;
- Circulation structure;
- Preload or axial-clearance requirement.
A nut marked for a 5 mm lead screw cannot normally be installed on a 10 mm lead screw, even if the nominal shaft diameter is the same. The internal raceway and ball circulation path will not match.
For replacement orders, the correct question is usually:
What Is Ball Screw Pitch?
Pitch is the axial distance between corresponding points on two adjacent thread grooves. It describes the spacing of the helical thread.
If the axial distance from one groove to the next corresponding groove is 5 mm, the thread pitch is 5 mm.
Pitch is a geometric feature of the screw and matching nut raceway. It should not be confused with:
- Ball diameter;
- Screw nominal diameter;
- Nut flange-hole spacing;
- Ball-circuit spacing;
- Lead accuracy;
- Axial clearance.
What Is Ball Screw Lead?
Lead is the axial distance travelled by the nut during one complete revolution of the screw. If the nut rotates while the screw remains fixed, lead still describes the relative axial movement produced by one complete rotation.
Common model examples include:
| Model Example | Nominal Diameter | Nominal Lead | Travel per Revolution |
|---|---|---|---|
| SFU1204 | 12 mm | 4 mm | Approximately 4 mm |
| SFU1605 | 16 mm | 5 mm | Approximately 5 mm |
| SFU2510 | 25 mm | 10 mm | Approximately 10 mm |
| SFE2525 | 25 mm | 25 mm | Approximately 25 mm |
The movement is described as approximate because the actual travel is affected by the screw's lead accuracy and operating temperature. The nominal lead remains the model value used for speed and transmission calculations.
When Are Pitch and Lead the Same?
Pitch and lead are the same in a single-start thread. A single-start screw has one continuous helical thread around the shaft.
For a single-start ball screw:
Therefore, if a single-start screw has a pitch of 5 mm, one complete revolution produces 5 mm of axial movement.
This is why pitch and lead are often used interchangeably in everyday ball screw enquiries. The wording may not cause a problem when both parties are discussing a standard single-start model, but using "lead" is more accurate when specifying travel per revolution.
When Are Pitch and Lead Different?
Pitch and lead differ in a multi-start screw. A multi-start thread contains two or more helical thread paths beginning at different positions around the shaft.
The relationship is:
For example, a double-start screw with a 5 mm pitch has:
The nut therefore travels 10 mm during one revolution, not 5 mm.
Multi-start structures may be used to obtain a larger lead while maintaining a practical thread form. However, the number of starts should not be assumed from the model appearance. It must be confirmed from the manufacturer's drawing or specification.
The Nut Model Usually States Diameter and Lead
In common ball screw model designations, the first number normally indicates nominal screw diameter and the second number indicates nominal lead.
Examples:
- 1605: 16 mm diameter and 5 mm lead;
- 1610: 16 mm diameter and 10 mm lead;
- 2005: 20 mm diameter and 5 mm lead;
- 2020: 20 mm diameter and 20 mm lead;
- 2510: 25 mm diameter and 10 mm lead;
- 2525: 25 mm diameter and 25 mm lead.
This convention is useful for preliminary identification, but it does not provide every necessary dimension. Two nuts with the same diameter and lead may still differ in:
- Nut series;
- Flange shape;
- Overall length;
- Number of ball circuits;
- Ball-return structure;
- Preload;
- Mounting-hole arrangement;
- Raceway profile.
Can Lead Be Identified from the Nut's Appearance?
No. The external shape of a ball nut does not reliably reveal its lead. The internal helical raceway and circulation components determine which screw it matches.
A rotating ball nut still requires a screw with the correct diameter, lead, raceway and thread direction.
Flange dimensions and appearance do not show whether the matching lead is 5 mm, 10 mm or another value.
For replacement work, use the complete nut marking, original drawing or matching screw specification. Measuring the flange and bore with a caliper is not enough to identify the internal lead accurately.
How Lead Affects Linear Speed
A larger lead produces more linear movement for each screw revolution. Linear speed can be calculated from screw speed and lead:
When RPM is expressed in revolutions per minute and lead in millimetres per revolution, the result is millimetres per minute.
| Lead | Screw Speed | Theoretical Linear Speed |
|---|---|---|
| 5 mm | 1,000 rpm | 5,000 mm/min |
| 10 mm | 1,000 rpm | 10,000 mm/min |
| 20 mm | 1,000 rpm | 20,000 mm/min |
These values are theoretical travel speeds. The actual permissible speed must still be checked against screw critical speed, nut circulation speed, support bearings, lubrication and installation accuracy.
How Lead Affects Required Screw RPM
For a specified linear speed, a larger lead reduces the required screw RPM:
For example, to produce 20,000 mm/min:
- A 5 mm lead requires 4,000 rpm;
- A 10 mm lead requires 2,000 rpm;
- A 20 mm lead requires 1,000 rpm.
This is one reason large-lead screws are considered for rapid-feed axes. Lower screw RPM can help reduce the risk of approaching shaft critical speed, especially on longer systems.
However, a larger lead is not automatically the better choice. Motor torque, acceleration, control resolution and ball-circulation structure must also be checked.
How Lead Affects Driving Torque and Thrust
For the same input torque, a smaller lead generally produces greater theoretical axial thrust. A larger lead normally requires more motor torque to produce the same axial force.
Therefore:
- A small lead can be useful where thrust and fine mechanical movement are priorities;
- A large lead can be useful where rapid linear movement is required;
- The motor must be sized from the actual load, acceleration and lead;
- Ball screw efficiency and preload must be included in the torque calculation;
- Vertical axes must also include gravity and holding requirements.
It is too simple to state that a large-lead ball screw cannot carry a heavy load. Load capacity is also determined by diameter, ball size, number of circuits, nut design and dynamic and static load ratings.
Does a Smaller Lead Always Provide Better Accuracy?
No. A smaller lead can provide finer theoretical movement for each motor revolution or encoder pulse, but it does not independently define the ball screw's lead accuracy.
Positioning performance also depends on:
- Ball screw accuracy grade;
- Motor encoder resolution;
- Controller command resolution;
- Nut preload or axial clearance;
- Support-bearing rigidity;
- Coupling stiffness;
- Thermal expansion;
- Installation alignment;
- Feedback and compensation method.
A 10 mm lead C5 ground ball screw may have better travel accuracy than a 5 mm lead C7 rolled ball screw. Lead and accuracy grade should therefore be specified separately.
Lead Is Not the Same as Lead Accuracy
Lead states the nominal travel per revolution. Lead accuracy states how closely the actual travel follows that nominal value over a defined length.
For example, "10 mm lead" does not mean the positioning error is 10 mm or that every revolution produces exactly 10.000 mm under all conditions. It identifies the nominal transmission ratio.
| Term | Meaning | Example |
|---|---|---|
| Pitch | Axial spacing between adjacent corresponding thread grooves | 5 mm thread pitch |
| Lead | Nominal axial travel during one revolution | 10 mm/revolution |
| Lead accuracy | Permitted difference between nominal and actual travel | C5 or C3 over a specified travel |
| Axial clearance | Lost axial movement during reversal | Specified clearance or preload condition |
How to Choose the Correct Ball Screw Lead
The correct lead should be selected from the complete motion requirement rather than from speed alone.
Check the following conditions:
- Required maximum linear speed;
- Motor maximum and continuous RPM;
- Moving mass;
- Acceleration and deceleration;
- External axial force;
- Horizontal, vertical or inclined installation;
- Positioning resolution;
- Accuracy and repeatability requirements;
- Screw diameter and unsupported length;
- Critical-speed limit;
- Nut circulation-speed limit;
- Available nut and flange dimensions.
A practical initial calculation is:
- Define the maximum required linear speed.
- Confirm the motor's usable maximum speed.
- Estimate the minimum lead needed to produce the required speed.
- Calculate the motor torque required for the selected lead.
- Check positioning resolution and control performance.
- Check screw critical speed and nut circulation speed.
- Confirm that the selected diameter-lead combination is available.
Can a Replacement Nut Be Selected by Lead Alone?
No. Lead is essential, but it is only one matching condition.
For a replacement ball nut, confirm:
- Complete nut model;
- Screw nominal diameter;
- Lead;
- Right-hand or left-hand thread;
- Nut series and circulation structure;
- Nut body length;
- Flange shape and thickness;
- Mounting-hole dimensions;
- Ball-circuit quantity;
- Preload or axial clearance;
- Condition of the existing screw raceway.
Even two nuts marked "1605" may not be interchangeable if their raceway geometry, return system, preload or flange dimensions differ.
If the old screw is worn or damaged, replacing only the nut may not restore smooth movement or original accuracy. A matched screw-and-nut assembly may be more reliable.
Common Pitch and Lead Mistakes
- Calling travel per revolution "pitch" in every case: Lead is the more accurate term.
- Assuming pitch always equals lead: They differ in multi-start screws.
- Ordering a nut by diameter only: A 16 mm screw may have a 4, 5 or 10 mm lead.
- Ordering by lead only: Diameter, raceway and nut structure must also match.
- Judging lead from the flange: External appearance does not reveal the internal helix.
- Assuming a larger lead cannot carry heavy loads: Check the actual nut ratings and circuit design.
- Assuming a smaller lead is automatically more accurate: Lead accuracy grade is a separate specification.
- Ignoring motor torque: A larger lead normally requires more torque for the same thrust.
- Ignoring screw RPM: A small lead may require excessive rotational speed.
What Information Should Be Sent to DLY?
To confirm a ball screw nut lead or replacement model, provide:
- Complete screw or nut model;
- Screw diameter;
- Lead or measured travel per revolution;
- Thread direction;
- Nut body and flange dimensions;
- Mounting-hole layout;
- Required speed and stroke;
- Axial load;
- Accuracy and preload requirement;
- Clear photos of the nut and screw;
- Original drawing where available;
- Whether the nut must match an existing screw shaft.
For available structures and common lead combinations, review the DLY ball screw nut range.
For fast-feed systems requiring a larger travel per revolution, see the DLY large-lead ball screw options.
To understand the difference between nominal lead and travel error, read What Is the Lead Accuracy of Ball Screws?
Final Answer
The value commonly called the "pitch of a ball screw nut" is usually the lead of its matching screw-the nominal axial distance travelled in one revolution.
For a single-start screw, pitch and lead are equal. For a multi-start screw, lead equals pitch multiplied by the number of thread starts. The ball nut must match the screw's diameter, lead, thread direction, raceway geometry and circulation structure.
Do not select a replacement nut from the word "pitch" or the flange appearance alone. Send DLY the complete model, screw diameter, lead, thread direction, nut dimensions and existing screw information for confirmation.
