Follower arm · Step 21 of 26 · F-060

Attach the gripper body to the motor 5 horn

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Do this

Set the gripper body onto motor 5's
horn
Horn. The metal disc that fits on the end of a motor; printed parts screw onto it. Each motor ships with two, one with gear teeth around its edge for the driven end and one plain disc for the other end.Source: waveshare.com · lerobot/docs/source/so101.mdx#joint-1
and screw it on with 4
M3x6.
M3x6. A screw size. M3 means a 3 mm thread, 6 means 6 mm long. It has a machine thread and goes into the threaded holes of a horn; the same size holds each printed part to its horn.Source: mantech.co.za · lerobot/docs/source/so101.mdx#joint-1
src
- lerobot/docs/source/so101.mdx#gripper--handle — Follower: "Attach the gripper to motor 5, attach it to the motor horn on the wrist using 4 M3x6mm screws."
- check — Gripper body seated on the horn with 4 M3x6.
- parts.yaml · wrist-roll-follower-so101 — Follower wrist roll (gripper body)
- servos.yaml · follower/wrist_roll — ID 5 · STS3215 1:345 · Feetech STS3215 servo, 7.4V, 1:345 gear (C001)

Done when The gripper body sits on the horn with its 4 screws.

lerobot/docs/source/so101.mdx#gripper--handleFollower: "Attach the gripper to motor 5, attach it to the motor horn on the wrist using 4 M3x6mm screws."

waveshare.comFollower step 16

SO-ARM100/STEP/SO101/SO101 Assembly.stepplacement check (viewer/public/geometry/placements.json): Wrist_Roll_Follower_SO101 carries the stepped r10/r12/r13.24 recess at its origin and the servo-5 drive horn sits in it

Check: Gripper body seated on the horn with 4 M3x6.

Motor slot: wrist_roll · ID 5 · STS3215 1:345 · 7.4V servo on a 5V supply; 12V servo on a 12V 5A+ supply (optional variant);

How we placed it: Part role confirmed by placement in the upstream assembly STEP: Wrist_Roll_Follower_SO101 carries the stepped r10/r12/r13.24 recess at its origin and the servo-5 drive horn sits in it.

Motor 5 · wrist roll

The motor you labelled 5: STS3215 motor,

1:345

Gear ratio. The number on the motor's label, such as 1:345. The motor inside turns 345 times for one turn of the output. The follower arm uses 1:345 at all six joints. The leader arm mixes 1:191, 1:345 and 1:147, so check the label before fitting a motor.Source: lerobot/docs/source/so101.mdx#step-by-step-assembly-instructions · SO-ARM100/README.md#sourcing-parts

gear, code C001. details

You need

Gripper bodyFollower wrist roll (gripper body) wrist-roll-follower-so101 details
STS3215 motor, 1:345 gear, code C001Feetech STS3215 servo, 7.4V, 1:345 gear (C001) servo-sts3215-c001-345
approximation3D stand-in
Stand-in shape: the 3D geometry or placement is not measured from the real part.
Qty 7 is the two-arm build (6 follower + 1 leader). A 12V variant with 30 kg.cm stall exists for the follower only and needs a 12V 5A+ supply (README). Includes two horns and a 3-pin cable per the assembly texts; kit contents are not itemised upstream. Geometry: the upstream repo's own simplified body `STEP/SO100/STS3215_03a.step` (Apache-2.0, single solid drawn to the datasheet, D-007 for where they differ) with its fused horn plates cut off and the datasheet ø6 x 3.4 output boss added, posed on the embedded vendor model's transform; the vendor mesh is not redistributed.
details
M3x6 screwM3x6 screw m3x6 ×4 details
Phillips screwdriver #0 · PH0 tool details
Phillips screwdriver #1 · PH1 tool details

Sources (3)

lerobot/docs/source/so101.mdx#gripper--handle — Follower: "Attach the gripper to motor 5, attach it to the motor horn on the wrist using 4 M3x6mm screws."
waveshare.com (retrieved 2026-09-07) — Follower step 16
SO-ARM100/STEP/SO101/SO101 Assembly.step — placement check (viewer/public/geometry/placements.json): Wrist_Roll_Follower_SO101 carries the stepped r10/r12/r13.24 recess at its origin and the servo-5 drive horn sits in it

How we placed it

Part role confirmed by placement in the upstream assembly STEP: Wrist_Roll_Follower_SO101 carries the stepped r10/r12/r13.24 recess at its origin and the servo-5 drive horn sits in it.