At a Glance

> Check the old cap: Confirm the existing cap number, thread size, and hub style before ordering.
> Inspect the sealing surface: Clean the hub threads and sealing area before installing the replacement cap and O-ring.
> Use the correct tool: The included wrench helps install and remove the cap without relying on improvised tools.
> Thread Check: Confirm the 3.5"-12 threaded cap specification before ordering.
> Seal Check: Make sure the O-ring seats correctly and the center plug is fully installed.
Brand: R & P Carriages
SKU: 21-88-BILLET-WRENCH-KITX2

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 Cap Service Kit

Two - Billet Aluminum Trailer Oil Bath Caps 3.5"-12 Thread with Wrench

Two billet aluminum oil bath caps with matching service wrench for compatible 3.5"-12 threaded oil bath hub applications. Commonly used on Dexter 9K–10K post-July 2009 axle applications where the existing cap, hub, and thread size match.

Part Number: 21-88-BILLET-WRENCH-KITX2 3.5"-12 Thread 2 Caps + Wrench

Key Measurements & Specs

Specification	Detail
Part Number / SKU	21-88-BILLET-WRENCH-KITX2
Selling Brand	R&P Carriages curated service kit
Product Type	Billet aluminum oil bath cap kit
Thread Specification	3.5"-12 threaded oil cap application
Material	Billet aluminum caps
Quantity Included	2 oil bath caps, 2 center plugs, 2 O-rings, and 1 billet wrench

Fitment / Application

Category	Details
Trailer / System	Oil bath trailer hub applications
Primary Application	Compatible with Dexter 9K–10K post-July 2009 applications where the 3.5"-12 oil cap fitment matches
Fitment Method	Verify existing oil cap number, thread diameter, thread pitch, hub style, and sealing components before ordering
Important Note	Application reference only. This listing is not claiming a Dexter OEM-branded part unless specifically verified on the product packaging.

Top Features

Feature	Buyer Benefit
Billet Aluminum Caps	Durable cap construction for oil bath hub service and replacement
3.5"-12 Thread Fit	Matches compatible threaded oil bath hub applications using this thread specification
Pair Kit	Includes two caps for servicing both sides of a compatible axle setup
Wrench Included	Includes matching billet wrench for cap installation and removal

Overview

This R&P Carriages curated kit includes two billet aluminum 21-88 style oil bath caps, two center plugs, two O-rings, and one billet wrench. It is intended for compatible 3.5"-12 threaded oil bath hub applications, including listed Dexter 9K–10K post-July 2009 axle applications where the buyer verifies the existing cap, hub, and thread specifications before installation.

R&P Service Insight

Oil bath caps are small parts, but they are critical to hub lubrication. A correct cap must match the hub thread, seal properly, and retain lubrication without cross-threading or damaging the O-ring during installation.

Check the old cap: Confirm the existing cap number, thread size, and hub style before ordering.
Inspect the sealing surface: Clean the hub threads and sealing area before installing the replacement cap and O-ring.
Use the correct tool: The included wrench helps install and remove the cap without relying on improvised tools.

R&P Knowledge Hub

Compatibility: Designed for compatible 3.5"-12 threaded oil bath hub applications. Verify before ordering if your axle, hub, or cap has been changed from the original configuration.

Vehicle / System Fit: Commonly used with listed Dexter 9K–10K post-July 2009 oil bath hub applications where measurements match.

Installation Notes: Replace the O-ring and center plug during cap service when included. Do not force the cap if threads do not start cleanly.

Performance Insight: The oil cap helps retain hub lubricant and protect the bearing assembly. Proper fit and sealing are essential for oil bath hub reliability.

Brand & Fitment Note

Selling Brand: R&P Carriages curated service kit

Application Reference: Dexter references are used for compatibility and application identification only.

What This Means: This listing is for a billet aluminum oil bath cap kit for compatible applications, not a guaranteed Dexter OEM-branded item unless specifically stated and verified.

Before Ordering: Verify the existing cap number, thread size, hub type, axle rating, oil bath setup, O-ring fit, and included components before installation.

R&P Repair Insight

When replacing oil bath caps, fitment problems usually come from mismatched thread size, damaged hub threads, missing sealing components, or assuming all high-capacity Dexter-style oil bath caps are the same.

Thread Check: Confirm the 3.5"-12 threaded cap specification before ordering.
Seal Check: Make sure the O-ring seats correctly and the center plug is fully installed.
Hub Check: If the hub threads are damaged or contaminated, correct that issue before installing the new cap.

Features

Billet Aluminum Construction

Solid billet aluminum cap design for compatible oil bath hub service and replacement.

3.5"-12 Thread Specification

Built for compatible threaded oil bath hub applications using the 3.5"-12 cap size.

Two-Cap Service Kit

Includes two oil bath caps so both sides of a compatible axle setup can be serviced together.

Wrench Included

Comes with one matching billet wrench for installation and removal of compatible 2.5" hex caps.

Included Components

Part Number	Quantity	Item
21-88	2	Billet aluminum oil bath cap, 3.5"-12 thread
046-032-00	2	Center plug
010-050-00	2	O-ring
Billet-Wrench-2.5	1	Billet aluminum wrench for 2.5" hex caps

Important Fitment Note: Verify all measurements, thread size, axle application, hub style, sealing components, and included parts before installation. Dexter references describe application fitment only and do not indicate OEM-branded status unless specifically verified.

Shop More 21-88 Oil Cap Options

21-88-BILLET-WRENCH-KITX2 billet aluminum oil bath cap kit pair 3.5-12 thread oil cap Dexter application 9K 10K post July 2009 oil bath hub cap replacement 21-88 cap set with wrench 046-032-00 center plug 010-050-00 O-ring billet wrench trailer hub oil cap service kit R&P Carriages

Two - Billet Aluminum Trailer Oil Bath Caps 3.5"-12 Thread with Wrench (21-88-BILLET-WRENCH-KITX2)