> ## 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.

# Top rail install

> Bolt the top crossbar onto the gantry to lock the frame rigid.

## Capping the frame

The **top rail** is the crossbar that connects the two uprights and makes the whole frame rigid. It comes pre-fitted with four screws. This is an easy, satisfying step.

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<Info>
  For this step you need **four M5x25 screws** (from the bag of five) and the **number 5 Allen wrench** (the largest).
</Info>

## Step-by-step

<Steps>
  <Step title="Find the indented side">
    One side of the top rail has **indentations** (grooves) and one is smooth. The **indented side must face up** toward the ceiling so the screw heads can sit flush.
  </Step>

  <Step title="Set it on top">
    Place the rail across the top of the two uprights, indented side up.
  </Step>

  <Step title="Start all four screws">
    Drop an **M5x25** into each of the four holes and thread each a few turns before fully tightening any - this keeps everything aligned.
  </Step>

  <Step title="Tighten in a pattern">
    Work around the four screws, tightening each fully with the number 5 Allen wrench. The heads should sink flush into the track.
  </Step>
</Steps>

<Warning>
  If the screws will not tighten all the way and sit on top of the bar, the rail is **upside down**. Flip it so the indented side faces up.
</Warning>

<Check>
  The top rail is bolted on with all four M5x25 screws flush and tight. The frame is now rigid - you should be able to pick the whole printer up by the top rail.
</Check>

## Up next

Next you snap on the plastic **end caps** to cover the sharp rail ends.