Product Description
Shimano 10DMJ Oscillating Gear (16NAS2500FB)
The Shimano 10DMJ Oscillating Gear is a core component of the spool stroke mechanism in the Nasci FB series of spinning reels. In Shimano’s "S-System" architecture, this gear is responsible for converting the rotational energy of the handle into the vertical "up-and-down" motion of the spool.
This gear features a specialized track or "cam" on its surface that guides the oscillation slider. By controlling the speed and consistency of the spool's travel, the 10DMJ ensures that the fishing line is wrapped evenly across the spool. If this gear becomes worn, chipped, or contaminated with sand, the spool may develop a "hitch" at the top or bottom of its stroke, or the line may begin to bunch up at one end of the spool.
Product Specifications
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Part Name: Oscillating Gear
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Part Number: 10DMJ
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Model Code: 16NAS2500FB
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Shimano Code: RD17841
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Material: High-Strength Engineering Polymer
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Function: Drives the vertical movement of the spool for uniform line lay.
Alternate Part Numbers
This part is commonly identified in technical service manuals and regional parts lists as:
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RD17841
Compatibility & Fitment
The 10DMJ (RD17841) is specifically designed for the 2500-size frame of the Nasci FB series. It is a direct factory fit for the following models:
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Shimano Nasci FB: NAS-2500FB, NAS-C3000FB, NAS-C3000HGFB
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Shimano Sahara FI: Fits select 2500/3000 models (Verify via RD code)
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Shimano Sedona FI: Fits select 2500/3000 models (Verify via RD code)
Key Features
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Precision Cam Track: Engineered to provide a smooth transition at the "turnaround" points of the spool stroke, reducing line stacking.
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Vibration Dampening: The composite material is designed to operate more quietly than metal-on-metal gear systems.
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Corrosion Proof: Being a non-metallic part, it is entirely immune to the salt-bridge corrosion that can seize internal spinning reel components.
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Direct OEM Replacement: Guaranteed to match the tooth pitch of the internal idle gears for a seamless, factory-smooth retrieve.
Installation & Maintenance
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Cleaning: Before installing a new 10DMJ gear, thoroughly clean the "pocket" in the reel body where the gear sits. Old grease mixed with metal shavings can quickly wear down the teeth of a new polymer gear.
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Lubrication: Use a light-to-medium synthetic grease. Shimano DG06 (Ship Grease) is the factory recommendation for oscillation gears to ensure they remain "sticky" enough to stay in the tracks but light enough for a smooth retrieve.
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Alignment: Ensure the Oscillating Slider (RD17842) is properly seated in the gear's cam track before closing the body side plate.
Pro Tip: If your spool has stopped moving entirely but the rotor still spins, check this gear first. Polymer oscillation gears are designed to be the "weak link" in the system—if the spool gets jammed, this gear will strip its teeth to protect the more expensive drive gear and pinion. You can view the full assembly order in the PDF schematics at www.reelschematic.com.
