iFJF Trailer Axle Oil Cap Kit 21-36 — 4-Pack Replacement for Dexter 9K/10K/12K/15K, O-Rings & Plugs

iFJF 4Pcs 21-36 Oil Cap Kit is a direct-fit replacement set of four 21-36 axle oil caps, O-rings, and rubber plugs built to restore proper sealing on compatible Dexter trailer axles.

This replacement kit supplies the 21-36 style oil caps designed to fit Dexter 9K (after 10-1-1989), 10K, 12K, and 15K axles—helping prevent grease and lubricant leaks at the hub opening. Each kit contains four oil caps with matching O-rings and rubber plugs so you can service both axles on a tandem or single-axle trailer in one job. Made from corrosion-resistant materials, the caps match the original part dimensions (4" outside diameter, 4"-12 thread, 1-1/2" depth) for reliable installation and fit.

Will these caps fit my Dexter axle model?

These oil caps are manufactured to replace Dexter part numbers 021-036, 021-036-00, 021-256, 021-256-00, 21-036, K21-301-00, and K71-148-00 and match the 21-36 size specification. They fit Dexter 9K (after 10-1-1989), 10K, 12K, and 15K axles—but they do not fit the 10K 2009 and newer general duty axles from Dexter #21-88.

• Fits: Dexter 9K (post 10-1-1989), 10K, 12K, 15K axles
• Not compatible with: 10K 2009+ Dexter #21-88 general duty axles
• Replaces: listed Dexter part numbers for direct swap

How do these caps hold up against corrosion and wear?

The iFJF caps are made from quality materials selected for light weight and resistance to rust and oxidation, giving long service life in typical road and marine trailer environments. They include new O-rings and rubber plugs to restore a full seal and reduce the likelihood of lubricant contamination or leakage.

• Corrosion-resistant finish for longer outdoor use
• O-rings included for improved sealing performance
• Durable construction resists cracking under normal service

What are the exact measurements and thread details?

The caps conform to the common 21-36 oil cap dimensions used on many Dexter axles. Knowing the dimensions and thread pitch helps ensure you purchase the correct replacement without modifying your hub assembly.

• Outside diameter: 4 inches
• Thread: 4"-12 standard thread pitch
• Depth: 1-1/2 inches

What comes in the package and how many axles can I service?

Each kit contains four oil caps plus matching sealing components, providing everything needed to replace caps on up to four hubs. That makes the kit convenient for single-axle owners replacing worn parts or tandem-axle owners completing both sides at once.

• Included: 4 x 21-36 oil caps
• Included: 4 x O-rings and 4 x rubber plugs for full sealing
• Enough parts to service up to four hubs or two tandem axles

Who is this for: Trailer owners, fleet managers, and DIY mechanics who need a dependable, direct-fit replacement for 21-36 Dexter-style oil caps will find this iFJF kit useful. It’s ideal for routine maintenance, restoring proper hub seals after wear or damage, and preparing trailers for seasonal use. If you’re unsure about compatibility, compare your current cap’s dimensions and Dexter part number to the specifications above before ordering.