Oil Bath Hub Service Kit
Two - Billet Aluminum 3.5" Oil Bath Caps – 21-88 Style – 10K General Duty Trailer Axles
Pair of machined billet aluminum oil bath caps for compatible 21-88 / 021-088-00 style threaded hub applications. Built as an aftermarket replacement option for buyers who want a stronger alternative to common plastic oil bath caps.
Part Number: 21-88 Billet-KITx2 3.5" Threaded Cap Pair: 2 Caps + Seals + Plugs
Key Measurements & Specs
| Specification |
Detail |
| Part Number / SKU |
21-88 Billet-KITx2 |
| Selling Brand |
R&P Carriages aftermarket service kit |
| Product Type |
Threaded oil bath cap pair with O-rings and rubber plugs |
| Cap Reference |
21-88 / 021-088-00 style oil bath cap application |
| Thread Outside Diameter |
3.5" |
| Thread Design |
12-thread style |
| Material |
Machined billet aluminum |
| Quantity Included |
Pair / 2 complete cap assemblies |
Fitment / Application
| Category |
Details |
| System |
Oil bath trailer hub / drum systems using 21-88 style threaded caps |
| Primary Application |
Commonly associated with Dexter 9K, 10K General Duty, and #13G threaded cap applications where 21-88 / 021-088-00 fitment is required |
| Production Note |
Verify fitment on applicable after-July-2009 General Duty hub assemblies before ordering |
| Drum Casting Check |
Compare existing hub/drum casting references such as 8-415 or 9-123 where applicable |
| Fitment Method |
Confirm the existing cap number, 3.5" thread outside diameter, thread style, O-ring, plug, and hub application |
| Important Note |
Not all 10K oil bath hubs use the same cap. Verify before ordering. |
Top Features
| Feature |
Buyer Benefit |
| Billet Aluminum Body |
Provides a stronger cap body than common plastic 21-88 style caps |
| Pair Kit |
Services both sides of one axle when the same cap application is used |
| Seals Included |
Includes matching O-rings and rubber plugs for cap assembly service |
| 21-88 Style Application |
Built for compatible threaded oil bath hubs using 21-88 / 021-088-00 style cap fitment |
Overview
This R&P Carriages 21-88 Billet-KITx2 includes two machined billet aluminum oil bath caps, two O-rings, and two rubber center plugs for compatible 21-88 / 021-088-00 style oil bath hub applications. This kit is intended as an aftermarket service replacement for compatible threaded oil bath hubs where the buyer has confirmed the cap size, thread style, and hub application.
R&P Service Insight
Oil bath hubs depend on a clean sealing surface, a properly seated O-ring, and a tight rubber center plug to retain lubricant around the bearings.
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Check the cap first: Match the existing cap to the 21-88 / 021-088-00 style application before ordering.
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Inspect the O-ring groove: Remove old oil, grit, and damaged seal material before installing the new O-ring.
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Confirm oil service: Fill and inspect the hub according to the axle or trailer manufacturer’s service procedure after installation.
R&P Knowledge Hub
Compatibility: Designed for compatible 21-88 / 021-088-00 style threaded oil bath cap applications. Verify before ordering if your axle, hub, drum, or cap style differs.
Vehicle / System Fit: Commonly associated with 9K to 10K General Duty oil bath trailer axle hub applications where the 21-88 style cap is used.
Installation Notes: Replace the cap, O-ring, and rubber plug together when the cap assembly is leaking, damaged, cracked, or being serviced.
Performance Insight: A properly sealed oil bath cap helps retain lubricant around the bearings. Billet aluminum construction adds cap-body durability compared with common plastic cap bodies.
Brand & Fitment Note
Selling Brand: R&P Carriages aftermarket billet oil bath cap kit.
Application Reference: Dexter, 21-88, 021-088-00, 010-163-00, 046-032-00, 8-415, and 9-123 are used as application and component reference terms for fitment matching only.
What This Means: This listing is for an R&P Carriages aftermarket billet aluminum service kit, not a guaranteed Dexter OEM-branded cap unless specifically stated on packaging or product labeling.
Before Ordering: Verify cap size, thread style, hub application, drum casting reference, O-ring reference, rubber plug reference, axle rating, and oil bath system before installation.
R&P Repair Insight
Oil bath cap problems are often caused by cracked plastic caps, hardened O-rings, damaged plugs, dirty sealing surfaces, or ordering the wrong cap style for the hub. Match the replacement kit carefully before disassembly.
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Cap Fit: Confirm the existing cap uses the 21-88 / 021-088-00 style threaded replacement.
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Seal Condition: Replace the O-ring any time the cap is removed if the seal is flattened, cut, brittle, or oil-soaked.
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Leak Check: After installation, inspect for seepage around the cap body and center plug before returning the trailer to service.
Features
Machined Billet Aluminum
Solid billet aluminum construction gives the cap body a more durable service profile than common plastic oil bath caps.
21-88 Style Replacement
Built for compatible threaded hubs that use the 21-88 / 021-088-00 style oil bath cap reference.
Complete Pair Kit
Includes two cap assemblies for servicing both hubs on one axle when the same 21-88 style application is used.
Sealing Components Included
Includes two O-rings and two rubber center plugs so the sealing components can be refreshed with the caps.
Included Components
| Quantity |
Item |
| 2 |
21-88 style billet aluminum oil bath caps, 3.5" threaded application |
| 2 |
010-163-00 style O-rings for 21-88 cap applications |
| 2 |
046-032-00 style rubber center oil plugs |
Important Fitment Note: Verify the existing cap number, 3.5" thread outside diameter, 12-thread style, O-ring style, rubber plug style, axle rating, hub type, drum casting reference, and oil bath system before installation. OEM and axle manufacturer names are used as application references only unless OEM status is specifically stated and verified.
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