During machine maintenance, replacement, or equipment retrofitting, it is common to find a ball screw without a clear model number, label, or supplier information. In this situation, the basic model can often be identified by measuring the screw diameter, pitch, number of starts, and lead.
This guide explains how to identify a ball screw model without markings, what measurements are needed, and what extra information should be checked before ordering a replacement ball screw.
A ball screw model is usually related to its nominal diameter and lead. For example, a model such as 2510 often means a 25 mm screw diameter and a 10 mm lead.
Why Ball Screw Model Identification Matters
When a machine stops because of a worn or damaged ball screw, the original model number may be missing. The label may be worn out, the machine supplier may no longer be available, or the old drawing may not be complete.
In this case, measuring the existing ball screw can help identify the basic model and prepare information for replacement, custom manufacturing, or technical verification. This is especially useful for CNC machines, automation equipment, packaging machines, linear modules, woodworking machines, and other industrial motion systems.
The goal is not only to find a similar diameter and lead. The final replacement ball screw must also match the original installation space, nut mounting method, end support, stroke length, accuracy requirement, and machine load condition.
What Can Be Identified Without Markings?
Without a visible model number, several important parameters can still be checked by direct measurement. But some details still need confirmation from drawings, machine structure, or supplier support.
| Can Be Identified by Measurement | Still Needs Confirmation |
|---|---|
| Screw diameter | Accuracy grade, such as C7 or C5 |
| Pitch or lead | Preload type |
| Number of starts | Nut type and flange dimensions |
| Basic model, such as 1605, 2510, or 3220 | End machining and support unit type |
| Approximate replacement direction | Total length, thread length, and effective travel |
Step 1: Measure the Ball Screw Diameter
The first step is to measure the nominal diameter of the ball screw using a vernier caliper. The diameter is usually the first part of the basic ball screw model.
Measure the distance across the screw at several positions and take the average. This helps reduce errors caused by wear, surface damage, or local measurement variation.
Common ball screw diameters include 12 mm, 16 mm, 20 mm, 25 mm, 32 mm, 40 mm, and 50 mm. This measurement determines the D parameter in the ball screw model.
Tip: If the screw surface is worn, dirty, or damaged, clean it first and measure at several points. Do not rely on only one measurement point.
Step 2: Measure the Thread Pitch
Next, measure the thread pitch. The pitch is the axial distance between two adjacent thread peaks or groove positions.
For easier measurement, you can measure the distance across several thread intervals and then divide by the number of intervals. This is more accurate than measuring only one small gap, especially for fine-pitch ball screws.
Common ball screw pitches include 5 mm, 10 mm, 16 mm, and 20 mm. This pitch measurement is important, but it should not be confused with lead, especially when the screw has more than one start.
Step 3: Determine the Number of Starts
Ball screws can be single-start or multi-start. The number of starts affects the lead, which is the linear travel distance of the nut when the screw rotates one full turn.
To check the number of starts, look at the end face of the screw and count the number of independent thread starts. A single-start screw has one thread start. A double-start screw has two. Some special screws may have three or four starts.
| Start Type | Number of Starts | Effect on Lead |
|---|---|---|
| Single-start | 1 thread | Lead equals pitch |
| Double-start | 2 threads | Lead equals pitch × 2 |
| Triple-start | 3 threads | Lead equals pitch × 3 |
| Quadruple-start | 4 threads | Lead equals pitch × 4 |
Step 4: Calculate the Lead
Once the pitch and number of starts are known, the lead can be calculated. Lead means how far the ball nut moves linearly when the screw rotates one full turn.
Lead = Pitch × Number of Starts
For example:
| Pitch | Number of Starts | Lead | Meaning |
|---|---|---|---|
| 5 mm | 2 | 10 mm | The nut moves 10 mm per screw rotation. |
| 10 mm | 1 | 10 mm | The nut also moves 10 mm per screw rotation. |
If the ball nut is still installed on the screw, there is another practical method. Mark the nut position, rotate the screw one full turn, and measure how far the nut moves. This directly gives the lead.
Pitch vs Lead: Common Confusion When Identifying Ball Screws
Pitch and lead are often confused, but they are not always the same.
Pitch is the axial distance between adjacent thread grooves. Lead is the distance the nut moves when the screw rotates one full turn.
For a single-start ball screw, pitch and lead are the same. For a multi-start ball screw, lead is larger than pitch because several thread starts work together.
This is why checking the number of starts is important. If you only measure the pitch but ignore the starts, the final model may be identified incorrectly.
Step 5: Confirm the Basic Ball Screw Model
After measuring the diameter, pitch, and number of starts, you can identify the basic ball screw model. In many common models, the first two numbers represent the screw diameter, and the last two numbers represent the lead.
For example:
| Measured Result | Basic Model | Meaning |
|---|---|---|
| Diameter 25 mm, lead 10 mm | 2510 | 25 mm screw diameter and 10 mm lead |
| Diameter 32 mm, lead 20 mm | 3220 | 32 mm screw diameter and 20 mm lead |
| Diameter 16 mm, lead 5 mm | 1605 | 16 mm screw diameter and 5 mm lead |
A basic model such as 2510 is useful, but it is still not enough for direct replacement. Ball screws with the same diameter and lead may have different nuts, flange sizes, accuracy grades, preload conditions, end machining, and total lengths.
What Else Should Be Checked Before Replacement?
For a complete replacement, more information should be confirmed. This helps prevent mismatch during installation and reduces the risk of ordering the wrong ball screw assembly.
1. Accuracy grade, such as C7 rolled or C5 ground.
2. Preload type, such as standard clearance, light preload, or double nut structure.
3. Ball nut type, including flange shape, mounting holes, and nut length.
4. Total screw length and threaded length.
5. Effective travel length required by the machine.
6. End machining dimensions for support units, bearings, coupling, and motor connection.
7. Installation direction, such as horizontal or vertical axis.
8. Working environment, load, speed, and lubrication condition.
If possible, provide photos of the old screw, ball nut, shaft ends, support units, and machine installation position. These details can help suppliers check compatibility more accurately.
Information to Send When Asking for Replacement
If you need a supplier to help identify or replace a ball screw without markings, prepare the following information:
| Information | Why It Matters |
|---|---|
| Measured diameter and lead | Identifies the basic model size. |
| Ball nut photos and dimensions | Confirms nut type, flange shape, and mounting size. |
| Total length and thread length | Ensures the replacement fits the machine stroke. |
| End machining drawing or photos | Checks support unit, bearing, coupling, and motor connection. |
| Machine type and axis direction | Helps judge load, accuracy, preload, and safety requirements. |
DLY Ball Screw Replacement Support
DLY supplies ball screws, ball nuts, ball screw support units, and customized end machining for CNC machines, automation equipment, packaging machinery, woodworking machines, and industrial motion systems.
For DLY ball screws, cold-rolled ball screws are generally C7 accuracy grade, while ground ball screws are generally C5 accuracy grade. DLY ball screw shaft material is S55C, and the ball nut material is 20CrMo.
If the old ball screw has no model number, you can send the measured diameter, lead, nut photos, total length, shaft end photos, and machine application. These details can help check whether a standard model or customized ball screw assembly is suitable.
Conclusion
Even without model markings, a ball screw can usually be identified by following a clear measurement process: measure diameter, measure pitch, count starts, calculate lead, and confirm the basic model.
However, the basic model is only the first step. A complete replacement also needs accuracy grade, preload type, nut dimensions, total length, end machining, support unit type, and application conditions.
For maintenance, replacement, or equipment retrofitting, accurate measurement and clear photos can greatly reduce communication time and help ensure that the new ball screw fits the original machine correctly.
Need Help Identifying a Ball Screw Model?
If your ball screw has no markings, you can send the measured diameter, lead, nut photos, total length, end machining photos, or machine application for replacement checking.
Email: export@dlybearing.com
