Billet Aluminum 3.5"-12 Trailer Cap Kit with O-Ring & Plug for Dexter 21-88 / 8-430 10K GD Hub
Heavy-duty billet aluminum oil bath cap kit for compatible 9,000 lb and 10,000 lb general-duty axle hub applications where the 3.5" thread outside diameter and 12-thread configuration match.
Overview
This R&P Carriages billet aluminum oil bath cap kit is a durable aftermarket replacement solution for compatible Dexter 21-88-style oil cap applications. It is designed for trailer hubs using a 3.5" thread outside diameter and 12-thread cap configuration, commonly found on listed 9,000 lb and 10,000 lb general-duty axle applications. The machined billet aluminum construction offers a stronger service replacement option when the original clear plastic cap is cracked, damaged, leaking, or no longer holding up in daily use.
R&P Service Insight
Oil bath hub caps are small parts, but they matter. A cracked or poorly sealing cap can allow oil loss, contamination, and hub service problems.
- Material Upgrade: Billet aluminum construction provides a more durable cap body than the commonly broken clear plastic style.
- Seal Check: This kit includes a new rubber O-ring and rubber fill plug for a cleaner service installation.
- Fit Verification: Confirm thread outside diameter, thread count, hub/drum casting, and axle rating before ordering.
R&P Knowledge Hub
Compatibility: Intended for compatible Dexter 21-88-style oil bath cap applications where the 3.5" thread outside diameter and 12-thread configuration match.
Vehicle / System Fit: Commonly used on 9,000 lb and 10,000 lb general-duty trailer axle hub applications with listed compatible hub and drum configurations.
Installation Notes: Verify the existing cap dimensions, hub/drum casting number, thread style, O-ring seat, and oil bath system condition before installation.
Performance Insight: A billet aluminum cap body helps reduce repeat failures associated with cracked or damaged plastic oil caps.
Brand & Fitment Note
Selling Brand: R&P Carriages
Application Reference: Dexter and Dexter 21-88 references describe compatibility target and application style only.
What This Means: This listing is for an R&P Carriages billet aluminum replacement oil bath cap kit, not a guaranteed OEM Dexter-branded cap unless specifically stated elsewhere and verified.
Before Ordering: Verify axle rating, hub/drum casting number, thread outside diameter, thread count, and included components before installation.
R&P Repair Insight
Before replacing an oil bath cap, inspect the full hub area. Oil loss may come from the cap, plug, O-ring, seal, hub face, or damage around the threaded area.
- Measure First: Confirm the cap thread outside diameter is 3.5" before ordering.
- Count Threads: Match the 12-thread cap design to the hub currently on the trailer.
- Inspect the Hub: Check for damaged threads, a rough sealing surface, or oil contamination before installing the new cap.
Features
Machined Billet Aluminum
Solid billet aluminum cap body offers a stronger service replacement option compared to commonly broken clear plastic oil caps.
3.5" Thread O.D.
Designed for compatible hub applications using a 3.5" thread outside diameter oil bath cap.
12-Thread Cap Design
Built for matching 12-thread cap applications where the hub thread pattern and cap configuration align.
Service Kit Components
Includes the billet aluminum oil bath cap, new rubber O-ring, and rubber fill plug for the cap assembly.
Specifications
| Specification | Detail |
|---|---|
| Part Number | 21-88 Billet-KIT |
| Brand | R&P Carriages |
| Product Type | Billet aluminum oil bath cap kit |
| Application | Trailer hub oil bath cap replacement for compatible 9K-10K general-duty axle applications |
| Material / Finish | Machined billet aluminum |
| Thread O.D. | 3.5" |
| Thread Design | 12-thread design |
| Replacement Reference | Replaces Dexter 21-88-style oil bath cap applications where dimensions and configuration match |
| Included Seal Components | New rubber O-ring and rubber fill plug included |
Fitment / Application
| Category | Details |
|---|---|
| Vehicle / System | Oil bath trailer hub systems |
| Primary Fit | 9,000 lb - 10,000 lb general-duty axle applications using the matching 3.5" oil cap configuration |
| Drum Casting Reference | 8-415 drums after July 2009 |
| Additional Fitment Reference | 8-430 hubs with 9-123 drums after April 2009 |
| Notes | Confirm hub casting, drum casting, thread outside diameter, thread count, and oil cap style before ordering. OEM names are used as application references only. |
Included Components
| Quantity | Item |
|---|---|
| 1 | Billet aluminum 3.5" oil bath cap |
| 1 | Rubber O-ring |
| 1 | Rubber fill plug |
