> ## Documentation Index
> Fetch the complete documentation index at: https://stem-docs.intellectualpoint.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Z-axis limit switch
> Install the Z-axis limit switch that sets the printer's lowest position, using T-nuts in the rail.
## Installing the limit switch
The **Z-axis limit switch** is an L-shaped board with a small click switch. It tells the printer where the bottom of its travel is, so the print head stops at the right height instead of crashing into the bed. It slides into the left rail, just behind the motor.
This part uses **T-nuts** (wing nuts) that lock into the rail slot, and the **number 4 Allen wrench**.
## How T-nuts work
A **T-nut** slides into the slot of an aluminum rail while vertical, then locks in place when you tighten its screw. This is how many parts attach to the frame without drilling.
## Step-by-step
With the number 4 Allen wrench, loosen each T-nut's screw **just enough** to rotate the nuts from horizontal to **vertical** so they can enter the rail slot. Do not remove them.
Hold the switch so the **click button points up** toward the ceiling, with the T-nuts vertical and facing the rail.
Insert the vertical T-nuts into the **outer rail slot** just behind the Z-axis motor and slide it down until a small plastic stop halts it.
Tighten both screws with the number 4 Allen wrench. The T-nuts rotate and grip the rail. Wiggle it to confirm it is locked, and press the click switch to confirm it moves freely.
The limit switch is locked in the left rail behind the motor, the click button faces up and clicks freely, and the switch does not wiggle.
If the switch will not tighten or keeps sliding, your T-nuts were too loose or too tight to grab the rail. Reset them to "barely snug," reinsert, and try again.
## Up next
Now the fun part - you start building the **extruder bar**, beginning with mounting the filament feeder.