# Z axis screw and nut sizes (X35)
**URL:** https://forum.onefinitycnc.com/t/z-axis-screw-and-nut-sizes-x35/26383
**Category:** Troubleshooting (X35/X50)
**Created:** [April 8, 2024, 8:16pm UTC](https://forum.onefinitycnc.com/t/z-axis-screw-and-nut-sizes-x35/26383 "2024-04-08T20:16:39Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@RedTonto](https://forum.onefinitycnc.com/u/RedTonto)
#### Post date: [April 8, 2024, 8:16pm UTC](https://forum.onefinitycnc.com/t/z-axis-screw-and-nut-sizes-x35/26383/1 "2024-04-08T20:16:39Z")
Hi from the UK,
On replacing the original spindle clamp to an 80mm for the new water cooled job I just purchased the ball bearings decided to exit the nut in fine style. Now looking at the parts list on OF’s wedsite it would appear that I need a new SFU1610 ball nut. (If I’m right the “16” refers to the screw diameter and the “10” refers to the thread pitch) Well on my X35 I would say that the screw diameter is 12 and the pitch 4 making it needing an SFU1204.
Is this correct?
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### Author:  [@TMToronto](https://forum.onefinitycnc.com/u/TMToronto)
#### Post date: [April 8, 2024, 8:36pm UTC](https://forum.onefinitycnc.com/t/z-axis-screw-and-nut-sizes-x35/26383/2 "2024-04-08T20:36:48Z")
… and I believe they only sell it with the ball screw as a set (for the Z16), not the nut on its own.
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### Author:  [@349iq2345](https://forum.onefinitycnc.com/u/349iq2345)
#### Post date: [April 8, 2024, 8:39pm UTC](https://forum.onefinitycnc.com/t/z-axis-screw-and-nut-sizes-x35/26383/3 "2024-04-08T20:39:22Z")
Hey David,
the original Z-16 Z assembly with its 16 mm diameter chrome-plated, hardened steel hollow shafts has a [1004 ball screw](https://forum.onefinitycnc.com/t/z-20-vs-z-16-z-slider-physical-differences/22370/1). You get a [replacement ball screw for this Z-16 with ball nut here](https://www.onefinitycnc.com/product-page/z-slider-ball-screw). The heavier and newer [Z-20 Z assembly](https://www.onefinitycnc.com/product-page/z-20-heavy-duty-z-slider) with 20 mm diameter chrome-plated, hardened steel hollow shafts has a 1610 ball screw.
- [Z-20 vs. Z-16 Z Slider Physical Differences](https://forum.onefinitycnc.com/t/z-20-vs-z-16-z-slider-physical-differences/22370)
By the way, the steeper pitch of the new Z-20 assembly led to the “spindle drop with gravity on initial estop or power loss issue” that did not occur with the less steep ball screw pitch on Z-16 assembly, and made Onefinity offer a [Z stepper with electromagnetic brake](https://www.onefinitycnc.com/product-page/elite-z-20-anti-drop-closed-loop-stepper-motor) for the Elite Series.
However on the Z-16 Z assembly, **you don’t need** to [change the ball screw and nut](https://www.youtube.com/watch?v=HMMI1K3SSfM) or the bearings when just replacing the 65 mm router mount by the optional [80 mm spindle mount](https://www.onefinitycnc.com/product-page/80mm-spindle-mount).
- [Support: Swapping the Spindle Mount on the Onefinity CNC](https://forum.onefinitycnc.com/t/support-swapping-the-spindle-mount-on-the-onefinity-cnc/6655)
Note that on the new Z-20 “heavy” slider, Onefinity does not offer a 80 mm spindle mount as a replacement part anymore. If you want a 80 mm mount on the Z-20, you got to order it with the 80 mm spindle mount from the beginning. If you order your Z-20 with 65 mm mount and want to upgrade to 80 mm later, you will be required to buy an entire Z-20 assembly ☹.
Z-16 Original/X-50 default settings for motor 3:
travel-per-rev = 4,
min-soft-limit = -133,
max-velocity = 3,
Z-20 “Heavy Duty” default settings for motor 3:
travel-per-rev = 10
min-soft-limit -160,
max-velocity = 7
(settings are for units=metric)