10S9M (RD18771 Idle Gear (Large)

Genuine Shimano Idle Gear — Large (part #RD18771, SKU 10S9M) — the intermediate gear in the oscillation mechanism that translates rotational motion from the drive train into the back-and-forth movement of the main shaft on Shimano spinning reels. The large idle gear meshes with the worm shaft or drive gear to create the oscillation pattern that lays line evenly across the spool. Worn or chipped idle gear teeth cause erratic oscillation, uneven line lay, and a rough feel during retrieve.
Cross-references with Shimano part number RD18771. OEM replacement restores the precise oscillation cycle for even line distribution and smooth cranking performance.
Available from Offshore Tackle & Repair in Stuart, FL — your trusted source for genuine Shimano spinning reel parts and professional reel service.