Four - Billet Aluminum Trailer Oil Bath Caps 4"-12 Thread with Wrench
Four-cap billet aluminum oil bath cap kit for 21-36 / 4"-12 threaded hub applications. Includes matching center plugs, O-rings, and a billet wrench for service-friendly installation and removal.
Key Measurements & Specs
| Specification | Detail |
|---|---|
| Part Number / SKU | 21-36-BILLET-WRENCH-KITX4 |
| Product Type | Billet aluminum oil bath cap kit with wrench |
| Cap Reference | 21-36 / 021-036-00 style oil cap applications |
| Thread Size | 4"-12 thread |
| Material | Billet aluminum caps |
| Quantity Included | 4 oil bath caps, 4 center plugs, 4 O-rings, and 1 billet wrench |
Fitment / Application
| Category | Details |
|---|---|
| System | Trailer oil bath hub applications using 4"-12 threaded caps |
| Primary Fit | 21-36 / 021-036-00 style cap applications where measurements match |
| Drum References | 9-44, 9-27, and 9-28 applications where the matching hub uses the 21-36 / 4"-12 oil cap |
| Fitment Method | Verify cap thread size, hub thread condition, plug size, O-ring fit, and original cap reference before ordering |
| Important Note | Application references are fitment guides only. Confirm your existing cap is the 21-36 / 4"-12 style before installation. |
Top Features
| Feature | Buyer Benefit |
|---|---|
| Four-Cap Kit | Service multiple hubs with one complete listing instead of ordering individual caps separately |
| Billet Aluminum Construction | Durable upgrade-style cap construction for oil bath hub service |
| 4"-12 Thread | Matches 21-36 style threaded oil bath cap applications where measurements match |
| Wrench Included | Provides a matched service tool for easier installation and removal of the billet caps |
Overview
This R&P Carriages four-cap kit is built for 21-36 / 4"-12 oil bath hub applications. The kit includes four billet aluminum oil bath caps, four center plugs, four O-rings, and one billet wrench, making it a practical service set for compatible heavy-duty trailer hub assemblies where the existing cap size and thread match.
R&P Service Insight
Oil bath caps are a small part of the hub assembly, but they matter. A poor seal, damaged O-ring, cracked plug, or wrong thread size can lead to oil loss and bearing service issues.
- Check the thread: Confirm the hub requires a 4"-12 threaded oil cap before ordering.
- Inspect the hub face: Clean the cap threads and sealing area before installing new caps and O-rings.
- Replace sealing parts together: Use the included O-rings and center plugs during cap replacement for a cleaner service job.
R&P Knowledge Hub
Compatibility: Designed for 21-36 / 021-036-00 style 4"-12 threaded oil bath cap applications where the hub and cap measurements match.
Vehicle / System Fit: Commonly used on compatible heavy-duty trailer oil bath hub systems that reference 21-36 style caps.
Installation Notes: Verify thread size, inspect the hub threads, lubricate the O-ring as appropriate for the hub service procedure, and avoid cross-threading during installation.
Performance Insight: A properly sealed oil bath cap helps retain hub lubricant, protect the bearing cavity, and reduce the risk of oil loss during trailer use.
Brand & Fitment Note
Selling Brand: R&P Carriages curated service kit
Application Reference: 21-36, 021-036-00, 010-050-00, 046-032-00, 9-44, 9-27, and 9-28 references are used for fitment identification only.
What This Means: This listing is for a billet aluminum oil bath cap kit assembled for compatible 21-36 style applications, not a guaranteed OEM-branded item unless specifically stated elsewhere.
Before Ordering: Verify your original cap reference, thread size, cap diameter, hub style, plug style, O-ring fit, and drum/hub application before installation.
R&P Repair Insight
The most common ordering mistake with oil bath caps is matching only the axle weight rating or drum reference while missing the actual cap thread size. Match the cap to the hub thread and original cap reference, not just the trailer rating.
- Confirm 4"-12: This kit is for 4"-12 threaded cap applications.
- Confirm 21-36 Style: Use this kit only where the 21-36 / 021-036-00 style cap is the correct match.
- Do Not Force Fit: If the cap does not start cleanly by hand, stop and re-check thread compatibility before tightening.
Features
Complete Four-Cap Service Kit
Includes four billet aluminum oil bath caps, four center plugs, four O-rings, and one billet wrench for compatible 21-36 applications.
4"-12 Threaded Design
Built for hubs requiring the 21-36 style 4"-12 threaded oil bath cap configuration.
Billet Aluminum Cap Construction
Machined billet aluminum cap design provides a sturdy service replacement option for compatible oil bath hub assemblies.
Installation Wrench Included
The included billet wrench helps with cap installation and removal, especially when servicing multiple hubs at the same time.
Included Components
| Part Number | Quantity | Item |
|---|---|---|
| 21-36 | 4 | Billet aluminum oil bath cap, 4"-12 thread |
| 046-032-00 | 4 | Center plug |
| 010-050-00 | 4 | O-ring |
| Billet-Wrench-2.5 | 1 | Billet aluminum wrench for 2.5" hex caps |
