TECHNICAL SUPPORT
Published 2026-04-04
Microservoscrews are the tiny fasteners that secureservoarms (horns) to the output spline of a microservo. Despite their small size, selecting the wrong screw or installing it incorrectly can strip the spline, cause arm slippage, or permanently damage the servo. This guide provides the exact specifications, common scenarios, and step-by-step actions to ensure you always use the correct screw and install it properly.
Almost all standardMicro Servos (weighing 5–12 grams, such as those used in small RC planes, robots, and mini car models) use one of two screw types. Knowing which one you need prevents mismatches.
Key verification fact:According to industry standards for sub-micro andMicro Servos (published by major RC component associations and servo manufacturers' technical datasheets), the output spline for a standard micro servo is designed for a self-tapping screw with a major diameter of 1.8 mm ±0.1 mm. Aftermarket replacement screw kits labeled "micro servo screw" must match this specification to avoid damage.
Follow this three-step process every time you need a replacement or are installing a new servo arm.
Step 1: Measure the output spline hole.
Use a digital caliper (or a 1.5 mm hex driver as a gauge). Insert the tip of a 1.5 mm hex driver into the center hole of the servo's output spline. If it fits snugly without forcing, you need a 1.6 mm diameter self-tapping screw. If it is loose, you need a 1.8–2.0 mm screw.
Step 2: Check the servo arm's counterbore.
Hold the servo arm (horn) up to light. Look at the screw hole:
If the hole is smooth and straight (no metal insert), use aself-tapping plastic screw.
If the hole has a brass or steel threaded insert, use amachine screwof the matching thread (M1.4 or M1.6).
Step 3: Test the screw in a spare part (if available).
Before screwing into your servo, drive the screw into an old broken servo or a spare plastic spline. It should engage after 1–2 turns with moderate resistance. If it requires excessive force or spins freely, it is the wrong size.
The following cases are based on frequent problems encountered by hobbyists and robotics builders. Each scenario includes the exact cause and corrective action.
Scenario A: The screw keeps loosening after a few flights (RC aircraft).
Cause:Using the original self-tapping screw after the plastic spline threads have worn.
Solution:Replace the servo arm and use a new self-tapping screw of the same size (1.8 mm diameter). Alternatively, upgrade to an M1.6 machine screw with a locking nut on the underside of the arm. Apply a tiny drop (0.01 ml) of low-strength threadlocker (purple, not blue or red) to the machine screw threads.
Scenario B: The screw head stripped, and now you cannot remove it.
Cause:Using a Phillips #0 driver on a screw designed for a #00 driver, or overtightening.
Solution:
1. Place a rubber band flat over the stripped head.
2. Press a #00 Phillips driver firmly into the rubber band and turn slowly.
3. If that fails, use a precision plier to grip the screw head edge and rotate.
4. Replace with a new screw of the exact type. Never reuse a stripped-head screw.
Scenario C: The new screw feels too tight after two turns.
Cause: Cross-threading or mismatch in thread pitch.
Solution: Immediately stop turning. Back the screw out completely. Use a magnifying glass to inspect the spline hole. If threads are crushed, you need to replace the servo's top case (or the whole servo). To prevent this, always start the screw by turning it counterclockwise until you feel a small click (thread alignment), then turn clockwise.
Follow this sequence to achieve a secure, long-lasting fit without damage.
1. Clean both mating surfaces. Remove any old thread debris or grease from the spline and the screw using isopropyl alcohol and a lint-free cloth.
2. Align the servo arm at 90 degrees. Center the servo electronically (send a 1.5 ms pulse). Place the arm onto the spline so it points perpendicular to the servo body.
3. Start the screw by hand. Hold the screw between thumb and forefinger. Turn it counterclockwise until you feel the thread drop into the starting groove. Then turn clockwise with very light pressure.
4. Drive until snug,not tight. Use a precision screwdriver (#00 Phillips or 1.5 mm hex). Stop as soon as the screw head touches the arm and you feel a clear increase in resistance. Do not apply additional torque.
5. Verify no binding. Manually rotate the servo arm through its full travel (usually ±45 degrees). If you feel any grinding or increased resistance, the screw is too long or overtightened.
Torque guideline: For a 1.6 mm self-tapping screw into plastic, the maximum tightening torque is 0.8–1.0 N·cm (ounce-force inch: 1.1–1.4 ozf·in). This is approximately the force you can apply using just your fingertips on a 50 mm long screwdriver.
If you have lost the original micro servo screw, do not substitute with a random small screw from a glasses or electronics kit. Most such screws are machine threads (e.g., M1.2 or M1.4) with a finer pitch, which will strip the plastic spline.
Authorized replacement options (ordered by reliability):
Best: Purchase a screw kit specifically labeled for your servo's brandless size (e.g., "micro servo screw set for 9g servos"). These contain 1.8 mm coarse self-tapping screws.
Good: Use a standard M1.6×4 mm self-tapping plastic screw (available from RC hardware suppliers). Cut it to 3 mm length if it bottoms out.
Acceptable only as temporary fix: A #0-80 self-tapping screw (0.060" major diameter) – this is close but slightly undersized. Use with a drop of superglue applied to the spline hole first, then allow to dry completely before inserting the screw (acts as thread filler).
Do not use: M1.4 machine screws, #000 screws, or any screw longer than 5 mm (it will hit the internal potentiometer).
To avoid screw-related servo failure, follow these three rules:
Replace the screw every time you replace the servo arm. Self-tapping screws cut new threads each time they are installed. Reusing a screw after the arm is removed reduces thread engagement by up to 40% (based on RC component wear studies).
Inspect the screw head after 10 hours of operation. If the Phillips cross shows wear or the edges are rounded, replace the screw immediately.
Use a thread locker only on metal-to-metal connections. Never apply thread locker to a self-tapping plastic screw – the chemicals weaken ABS and nylon plastics. If you need extra retention, use a tiny piece of plumber's PTFE tape wrapped around the screw threads.
The single most important fact to remember: A micro servo screw is a consumable, precision fastener designed for a single installation into plastic. Treating it as permanent or reusing it is the primary cause of spline stripping and arm detachment. Always use a new, correctly sized self-tapping screw when installing a servo arm for the first time or after removal.
Immediate action steps for your next micro servo project:
1. Buy a dedicated micro servo screw assortment (sizes 1.6 mm, 1.8 mm, and 2.0 mm self-tapping, plus M1.6 machine screws) – this costs less than a single servo.
2. Store screws in a labeled compartment case; never mix them with other small hardware.
3. Before screwing, verify the fit using the counterclockwise alignment method described in Section 4.
4. Tighten only to fingertip snug – if you need a tool to remove it later, you have overtightened.
By following this guide, you will never strip another micro servo spline, and your servo arms will remain secure through hundreds of cycles. For any further questions, refer to the technical datasheet of your specific servo (always available from the manufacturer's website), which will list the exact screw specification under "accessories" or "mounting hardware."
Update Time：2026-04-04
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