At a Glance

> Check the cap number: Match the replacement to the existing 21-88 style cap before ordering.
> Inspect the O-ring groove: Clean old oil, grit, and damaged seal material before installing the new O-ring.
> Confirm oil level: After service, fill and inspect the hub according to the trailer or axle manufacturer’s service procedure.
> Cap Fit: Confirm the existing cap uses the 21-88 style replacement before ordering.
> Seal Condition: Replace the O-ring any time the cap is removed for service if the seal is flattened, cut, or brittle.
Brand: R & P Carriages
SKU: 21-88-KIT

Before You Order

Match the part number, measurements and connection points that apply to your trailer.

Part Number	Match the number stamped on the original bearing or seal.
Dimensions	Measure the mating surfaces when a number is unavailable.
Hub / Axle	Use capacity as context, not as the only fitment check.

Product Details

Oil Bath Hub Service Kit

3.5" Oil Bath Cap Trailer Axle Dexter 9K 10K Kit with Plug and O-Ring – For 10K GD Axles

Complete oil cap service kit for 21-88 oil bath hub applications. Includes one 3.5" oil bath cap, one sealing O-ring, and one center oil plug for compatible 10K general duty axle setups.

Part Number: 21-88-KIT 3.5" Oil Bath Cap Cap + O-Ring + Plug

Key Measurements & Specs

Specification	Detail
Part Number / SKU	21-88-KIT
Product Type	Oil bath cap service kit
Cap Reference	21-88 / 021-088-00 style oil bath cap
Cap Size	3.5" threaded oil bath cap application
Seal / Plug References	010-163-00 O-ring and 046-032-00 center plug references
Quantity Included	One kit: 1 cap, 1 O-ring, 1 plug

Fitment / Application

Category	Details
System	Oil bath trailer hub / drum systems using 21-88 style caps
Primary Fit	Commonly used on 10K general duty axle applications after July 2009 where 21-88 cap fitment is required
Fitment Method	Verify the cap number, threaded cap size, hub application, and matching O-ring before ordering
Important Note	Not all 10K oil bath hubs use the same cap. Compare the existing cap and seal references before installation

Top Features

Feature	Buyer Benefit
Complete Service Kit	Includes the cap, O-ring, and center plug needed for a matched oil cap service replacement
21-88 Style Cap	Built for compatible hubs that use the 21-88 / 021-088-00 style oil bath cap
Oil Bath Sealing Support	Helps maintain oil retention when the cap, plug, and O-ring are properly installed
Shop-Friendly Kit	Keeps the common wear and sealing pieces together for quicker hub service work

Overview

This 21-88-KIT oil bath cap service kit is assembled for compatible trailer hub applications using a 21-88 style oil bath cap. The kit includes one oil bath cap, one O-ring, and one center plug, making it a practical replacement option when servicing a leaking, damaged, or worn oil bath cap assembly.

R&P Service Insight

Oil bath hubs depend on a clean sealing surface, a properly seated O-ring, and a tight center plug to retain lubricant around the bearings.

Check the cap number: Match the replacement to the existing 21-88 style cap before ordering.
Inspect the O-ring groove: Clean old oil, grit, and damaged seal material before installing the new O-ring.
Confirm oil level: After service, fill and inspect the hub according to the trailer or axle manufacturer’s service procedure.

R&P Knowledge Hub

Compatibility: Designed for compatible 21-88 oil bath cap systems. Verify before ordering if your axle, hub, or cap style differs.

Vehicle / System Fit: Commonly associated with 10K general duty trailer axle oil bath hub applications after July 2009 where 21-88 cap fitment is used.

Installation Notes: Replace the cap, O-ring, and center plug together when the cap assembly is leaking or when the plug and seal are worn.

Performance Insight: A properly sealed oil bath cap helps retain lubricant, protect bearing components, and reduce the chance of oil loss during trailer operation.

Brand & Fitment Note

Selling Brand: R&P Carriages curated service kit

Application Reference: 21-88, 021-088-00, 010-163-00, and 046-032-00 are used as application and component reference numbers for fitment matching.

What This Means: This listing is for one R&P Carriages oil bath cap service kit, not a guaranteed OEM-branded item unless specifically stated on packaging or product labeling.

Before Ordering: Verify cap size, thread style, hub application, O-ring reference, plug reference, and axle/hub compatibility before installation.

R&P Repair Insight

Oil bath cap leaks are often caused by an aged O-ring, damaged plug, cracked cap, dirty sealing surface, or incorrect cap selection. Match the replacement kit carefully before disassembly.

Cap Fit: Confirm the existing cap uses the 21-88 style replacement before ordering.
Seal Condition: Replace the O-ring any time the cap is removed for service if the seal is flattened, cut, or brittle.
Leak Check: After installation, inspect for seepage around the cap body and center plug before returning the trailer to service.

Features

Complete 3-Piece Kit

Includes one oil bath cap, one sealing O-ring, and one center oil plug for a complete cap assembly service.

21-88 Style Application

Designed for compatible hubs that use the 21-88 / 021-088-00 style oil bath cap reference.

Oil Bath Hub Service

Supports proper lubricant retention when installed on the correct hub with a clean sealing surface.

Fitment-Safe Replacement

Best matched by comparing the existing cap number, cap size, O-ring reference, and hub application before ordering.

Included Components

Quantity	Item
1	21-88 style oil bath cap, 3.5" application
1	010-163-00 style O-ring for 21-88 cap applications
1	046-032-00 style center oil plug

Important Fitment Note: Verify the existing cap number, threaded cap size, O-ring style, plug style, axle rating, hub type, and oil bath system before installation. 21-88 and related part numbers are used as application references for fitment matching.

Shop Related 21-88 Oil Cap Parts

21-88 oil bath cap kit, 21-88-KIT, 3.5 oil bath cap, 021-088-00 oil cap, 010-163-00 o-ring, 046-032-00 oil plug, 10K GD oil cap kit, trailer hub oil cap with o-ring and plug, oil bath hub cap replacement, 21-88 trailer axle oil cap kit

3.5" Oil Bath Cap Trailer Axle Dexter 9K 10K Kit with Plug and O-Ring – For 10K GD Axles (21-88-KIT)