The Futaba FU1K12901 D5mm horn circle is a two-piece accessory intended for replacing or fine-tuning the servo arm on the listed Futaba models. The item is sold without packaging or screws, so ensure you have suitable fasteners before attempting installation.
Compatibility care: the name indicates compatibility with S3103, S3107, 3153, 3156, and 3157. Always check spline engagement and the D5mm bore on your servo prior to fitting to ensure smooth operation. Do not assume it fits other servo types not listed.
Fitting procedure: remove the existing arm, align the D5mm horn on the servo spline, set the arm to neutral travel and secure it with an appropriate screw or retainer that you provide. This part functions as a linkage point useful for altering throw and mechanical advantage on small-scale models.
Use considerations: this is a basic replacement/tuning component and not a complete servo assembly. Consider threadlock where metal-to-metal contact exists and verify full-range movement after installation to prevent binding or excessive travel.
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