618-04125A, 618-04126A, 918-04125B, 918-04126, 918-04126B, 618-04126, 918-04126C, 918-04125C Spindle Assembly Fits for Cub RZT50 LT1050 Lawn Mower, Cub Troy Built Mustang Zero Turn 50" Mower Deck

What It Is

This is a replacement spindle assembly (the rotating shaft and housing that drives the mower blade) for 50-inch zero-turn mower decks. It fits Cub Cadet RZT50, LT1050, and Troy-Built Mustang models, as well as other 50" decks using these OEM-style spindles.

Fitment & Compatibility

Before buying, confirm:

• Deck width: 50 inches only. Will not fit 42", 46", or 54" decks.
• Model numbers: Check your mower’s model tag (under seat or on frame). This replaces OEM numbers 618-04125A, 618-04126A, 918-04125B, 918-04126, 918-04126B, 618-04126, 918-04126C, and 918-04125C.
• Measurements: Spindle housing diameter is ~2.5 inches; shaft diameter is 5/8 inch with a 3/16-inch keyway. Measure your old spindle to confirm.
• Bearing type: Uses two sealed ball bearings (6203-2RS) – verify your deck uses the same bearing size.
• OEM vs aftermarket: This is a generic aftermarket spindle, not OEM Cub Cadet/Troy-Bilt. It may have slightly different casting finish but functions identically.

Key Things to Know

• Quality: Users report good durability for the price, but some note bearings may wear faster than OEM on heavy commercial use. Fine for residential mowing.
• Installation: Straightforward – remove blade, pulley, and retaining ring; unbolt old spindle; install new one. Torque blade bolt to 70-90 ft-lbs.
• Common gotcha: The pulley bolt may be reverse-thread on some models (check before forcing). Also, the spindle housing may need a thin grease coating on the outside to prevent rust-seizing in the deck.
• Includes: Spindle assembly only – you reuse your existing blade, pulley, and hardware. No grease fitting.

Should You Buy It

Buy this if you have a 50" Cub Cadet or Troy-Bilt zero-turn with a failed spindle and want a budget-friendly, drop-in replacement for residential use. Skip it if you need commercial-grade longevity or an exact OEM match (buy genuine Cub Cadet instead).