# Step 3: Prepare the Bearing Housing

> Install three M4 square nuts, lightly tighten three M4x16 Socket bolts, and fit one flanged ball bearing in part 400_13C.

- Page: https://docs.menlo.ai/asimov/1/build/assembly-steps/left-arm-module/upper-arm-assembly/step-3
- Section: Asimov › Asimov 1 › Assemble Asimov 1 › Assemble › Left Arm Module › Upper Arm Assembly
- Previous: [Step 2: Attach the Shoulder Base and Route the Cable](https://docs.menlo.ai/asimov/1/build/assembly-steps/left-arm-module/shoulder-joint-assembly/step-2.md)
- Next: [Step 4: Prepare the Actuator Housing](https://docs.menlo.ai/asimov/1/build/assembly-steps/left-arm-module/upper-arm-assembly/step-4.md)

> [!IMPORTANT]
> **Assign actuator IDs before assembly**
>
> Assign and verify all 25 actuator IDs before assembling the robot. The robot will not work correctly with missing or incorrect IDs. IDs must be assigned one actuator at a time on the bench; you may need to disassemble the robot if you skip this step. See [Assign Actuator IDs](https://docs.menlo.ai/asimov/1/build/assembly-preparations/assign-actuator-ids.md).

## Parts needed

| Part | Count |
| - | -: |
| `400_13C` | 1 |
| M4 square nuts | 3 |
| M4x16 Socket bolt | 3 |
| Flanged ball bearing 4390N159 (part `400_19X`) | 1 |

## Instructions

1. Take part `400_13C` (the part with a side cable channel, not part `400_14C`) and place it on a flat surface with the inner hollow facing upward.

2. Place **3 of** M4 square nuts into the 3 slots on the surface of Part `400_13C`.

3. Using **3 of** M4x16 Socket bolts and lightly tighten it on the circumference of Part `400_13C` where you have previously inserted the square nuts to secure the square nuts in place first. If you over tighten, it will prevent the actuator from fitting in later on.

4. Place the flanged ball bearing 4390N159 into the bearing hole on Part `400_13C`.