The term Shimano Cog DX Chrome Plated primarily refers to the Shimano DX (CS-MX66) single-speed cassette sprocket, though it is occasionally used interchangeably with the threaded Shimano DX (SF-MX30) freewheel. Both are legendary, high-durability BMX racing and single-speed drivetrain components featuring a distinct, shiny chrome-plated finish.

1. Shimano DX CS-MX66 Cassette Cog (Splined)

This is a single-speed cassette sprocket designed to slide directly onto standard multi-speed freehub bodies or dedicated BMX cassette hubs.

Key Features:

• Interface Type: Splined interface matching traditional Shimano HyperGlide (HG) 7, 8, or 9-speed freehub bodies. It requires loose spacers and a lockring to secure it in place.
• Material: Hardened steel construction finished with an ultra-smooth chrome plating for optimal wear protection and weather resistance.
• Chain Compatibility: Engineered for narrow 1/2" x 3/32" chains (typical for 7/8-speed drivetrains), though it can track safely under wider 1/8" single-speed chains.
• Base Width: Built with a standard thin base profile. Note: If using this on an aluminum freehub body, ensure you utilize wide-base spacers to prevent the steel cog from cutting into the soft aluminum splines.

2. Shimano DX SF-MX30 Freewheel (Threaded)

If your wheel features a threaded hub instead of a splined cassette body, you are likely looking for this complete spin-on assembly.

Key Features:

• Interface Type: Threads directly onto standard English 1.37" x 24 TPI threaded hubs.
• Internal Mechanics: Features a robust internal spring and multi-pawl mechanism praised for its exceptionally quiet, smooth, and predictable engagement.
• Construction: Hard-wearing chrome-moly steel with a polished chrome exterior look.