5mm or 10mm Ball Screw Lead? The Question I Always Ask First

First, stop treating lead as a speed setting

Yes, lead is the linear distance the nut moves per revolution. 5mm lead means 5mm per rev. 10mm lead means 10mm per rev. So for the same motor RPM, the 10mm screw moves the axis twice as far.

But the screw doesn’t spin by itself. The motor has to push the load through that lead. And the larger the lead, the less mechanical advantage you have.

Think of it like gears on a bicycle. A bigger gear makes you go faster at the same pedaling speed, but it’s harder to pedal up a hill. A smaller gear gives you more force but requires faster pedaling to keep the same speed.

A ball screw lead works the same way. The 5mm lead is the smaller gear. The 10mm lead is the bigger gear.

So before asking “which one is faster,” ask “what am I actually pushing?”

The torque side is where most people get surprised

Here’s a simple way to look at it. If you keep the motor torque the same, doubling the lead from 5mm to 10mm roughly halves the axial force you get.

That means the 10mm screw needs a stronger motor to push the same load. Or it accelerates the same load more slowly. Or it struggles on a vertical axis where gravity is always pulling.

I’ve seen builders put a 10mm lead on a Z-axis with a 2.2 kW spindle, then wonder why the axis loses steps or faults out during rapids. The motor simply didn’t have enough torque to hold and move the weight through that larger lead.

On a light horizontal axis, 10mm can be great. The load is small, the speed is useful, and the torque requirement stays manageable. But on a heavy table or a vertical head, the 5mm lead suddenly looks much more practical.

So the first thing I check is the thrust requirement, not the speed requirement.

Start with the speed you actually need

A lot of machines don’t need to move as fast as the builder thinks. If your gantry is only 400mm long, does it really matter if you rapid at 10 m/min instead of 6 m/min? The axis reaches the end in a fraction of a second either way.

But on a long router table, speed matters. If you’re cutting full sheets of plywood and the axis has to traverse 2500mm between cuts, doubling the speed can save real time over an eight-hour day.

So before choosing lead, I ask the customer to give me a realistic rapid speed. Not “as fast as possible,” but a number they can actually use.

Then I calculate the screw RPM for both leads.

At 10 m/min:

• 5mm lead: 10,000 / 5 = 2,000 RPM

• 10mm lead: 10,000 / 10 = 1,000 RPM

At 15 m/min:

• 5mm lead: 3,000 RPM

• 10mm lead: 1,500 RPM

At 20 m/min:

• 5mm lead: 4,000 RPM

• 10mm lead: 2,000 RPM

That RPM number matters more than people think, especially as the screw gets longer. A 1500mm screw spinning at 4,000 RPM is going to whip and vibrate unless it’s very well supported. That’s a mechanical headache.

So if you need 20 m/min on a long axis, the 10mm lead might be the only practical option—not because it’s “better,” but because it keeps the screw speed down to a range the machine can handle.

Screw length is the hidden factor

Short screws are forgiving. A 300mm 5mm lead screw can spin fast without much trouble. The critical speed is high, and whip is barely a concern.

But long screws are a different story. Once you get past 800mm or so, the screw’s critical speed starts to drop quickly. The support arrangement matters. The end machining matters. The diameter matters. And the lead matters because it determines how fast you have to spin the screw to reach a given linear speed.

I’ve had designs where a 5mm lead was perfect for thrust, but the required RPM put the screw right at its critical speed limit. Switching to 10mm lead allowed the same linear speed at half the RPM, which made the whole axis more stable.

That’s not a compromise. That’s good engineering. Sometimes you choose the larger lead not because you want more speed, but because you want the same speed at a more manageable screw RPM.

What about positioning resolution?

This is where I see the most confusion.

People assume a 5mm lead gives you better resolution because the nut moves half as far per revolution. And in a very crude sense, that’s true. If you’re using a stepper motor with 200 steps per revolution and no microstepping, a 5mm lead gives you 0.025mm per full step, while a 10mm lead gives 0.05mm.

But most modern systems use microstepping or servo motors with high-resolution encoders. And the actual positioning error comes from a whole list of factors: lead accuracy, backlash, bearing play, guide alignment, thermal expansion, servo tuning. The lead size is only one small piece.

I’ve seen builders insist on a 5mm lead “for accuracy” and then install it on a machine with a twisted base and loose coupling. The 5mm lead didn’t save them. The machine still cut out of tolerance because the structure was flexing.

So if you’re worried about accuracy, first define what tolerance you need. If it’s ±0.02mm, we can talk about whether the lead matters. If it’s ±0.1mm, the lead probably isn’t your biggest problem.

Z-axes are a special case

A vertical axis is where the 5mm lead really shines. The motor has to support the weight of the head, spindle, and tooling—not just during cutting, but also when the axis is stopped.

If the lead is too large, the motor has to work harder just to hold position. During acceleration upward, the peak torque can be very high. A 10mm lead might still work if the motor is oversized, but a 5mm lead gives you more margin for the same motor.

That’s why you often see a 5mm lead on Z and a 10mm lead on X and Y. The X and Y axes move horizontally, where gravity isn’t constantly fighting the motion. The Z axis needs more mechanical advantage.

But again, it depends on the machine. A lightweight 3D printer or laser engraver might use 10mm on Z without any problem because the moving mass is tiny. The rule isn’t “always use 5mm on Z.” The rule is “check the load and torque before deciding.”

Acceleration is the part people forget

Everyone talks about top speed. But a machine that takes five seconds to reach that speed isn’t actually fast.

Acceleration requires torque. The motor has to spin up the screw, the coupling, the rotor, and the moving load. If the lead is large, the reflected inertia changes, and the torque requirement can go up unexpectedly.

I’ve seen axes that could reach 15 m/min but couldn’t accelerate quickly enough to make that speed useful on short moves. The machine spent most of its time ramping up and down. In that case, a smaller lead might have actually felt faster because the axis could get up to speed more quickly.

So when I compare 5mm and 10mm, I don’t just look at the top speed. I look at the motion profile. How long is the move? How often does the axis start and stop? How aggressive does the acceleration need to be?

A quick example

Let’s say you’re building a 600mm horizontal axis. Moving mass is 30kg. You want 15 m/min rapid speed. The motor is a 750W servo with a rated speed of 3000 RPM.

With a 5mm lead, you need 3000 RPM to hit 15 m/min. That’s right at the motor’s rated speed. It might work, but there’s no headroom.

With a 10mm lead, you need only 1500 RPM. That leaves plenty of speed margin. But now the motor has to produce twice the torque for the same thrust. If the load is light and the acceleration is moderate, that’s fine. If the load is heavy or the cutting forces are high, the motor might struggle.

So the answer isn’t obvious until you check the thrust and acceleration numbers. That’s the whole point.

What to send your supplier

When I get a request for a ball screw quote, I’m not impressed by a model number. I’m impressed by a simple list of requirements.

The best inquiries look like this:

• Axis: X-axis

• Travel: 600mm

• Moving mass: 30kg

• Max speed: 15 m/min

• Acceleration: 0.5G

• Orientation: horizontal

• Motor: 750W servo, 3000 RPM

• Required accuracy: ±0.02mm

• Duty cycle: 8 hours/day

That gives me enough to check the lead, diameter, support, and whether the motor can handle the job. If the numbers don’t work, I can tell you why and suggest an alternative.

If you just say “I need a 1605 ball screw,” I can’t help you much. You’ve already made the decision without knowing if it’s right.

The choice isn’t about which lead is better

At the end of the day, 5mm and 10mm leads are both useful. They’re just different tools for different situations.

A 5mm lead gives you more thrust and finer mechanical resolution. It’s great for vertical axes, heavy tables, and machines that need to push hard at moderate speeds.

A 10mm lead gives you more linear speed for the same screw RPM. It’s great for long, light, fast horizontal axes where the motor can handle the reduced mechanical advantage.

The mistake is choosing one because it “sounds right.” 5mm sounds precise. 10mm sounds fast. But sound isn’t engineering.

Do the basic calculations:

1. Required speed → screw RPM

2. Required thrust → motor torque

3. Acceleration → peak torque

4. Screw length → critical speed

Those four numbers will tell you more than any catalog comparison.

And if you’re still not sure, send those numbers to your supplier. A decent one will help you work through the trade-off instead of just taking your order.

That’s what separates a real ball screw selection from a guess.