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The CPI 1-1/4" FPT Threaded Raised Spinweld Fitting (Part #54LL / 500151) is the go-to solution for creating a secure, leak-resistant threaded connection on RV fresh water and holding tanks. The raised profile gives you extra clearance for fittings and hose connections, making installation and maintenance significantly easier than flush-mount alternatives.

Features & Specifications

Thread Size: 1-1/4" FPT (Female Pipe Thread)
Required Hole Size: 1-3/4" diameter
Fitting Style: Raised Spinweld
Connection Type: Threaded (FPT)
Application: RV Fresh Water Tanks & Holding Tanks
Material: Durable Plastic
Manufacturer: Custom Plastics (CPI)
Part Numbers: 54LL / 500151
Sold: Individually (Each)

Why Choose the CPI Part #54LL Raised Spinweld Fitting?

The raised spinweld design of the Part #54LL sets it apart from standard flush fittings. The elevated boss gives you more thread engagement depth and easier access for wrenches and hose connections — critical when working in tight RV tank compartments. The spinweld installation method creates a permanent, vibration-resistant bond directly to your polyethylene tank wall.

With a perfect 5.0-star rating from 7 verified buyers, the CPI 54LL is a proven performer trusted by RV owners and repair shops alike. It's the same OEM-grade fitting used by RV manufacturers during original production.

Compare CPI Spinweld & Raised Tank Fittings

Not sure which CPI fitting is right for your application? Use this table to compare thread size, hole size, and fitting style across the CPI lineup.

Part #	Thread / Size	Hole Size	Fitting Style	Best For	View Details
#55 (500108)	1-1/4" FPT	1-1/2"	Flat Spinweld	Low-profile flush mount applications	View #55
#54LL (500151) (This Product)	1-1/4" FPT	1-3/4"	Raised Spinweld	Raised clearance, easier hose/fitting access	Current Page
#61 (500121)	1-1/4" Spigot	1-1/2"	Spigot Spinweld	Slip-fit pipe connections (no threads)	View #61
#65M (500502)	2" Raised	2-1/2"	Raised Fitting	Larger diameter raised connections	View #65M

Tip: Choose a raised fitting when you need extra clearance for hose connections or when working in tight tank compartments. Use a flush fitting when tank wall space is limited.

Technical Specifications

Part Number: 54LL / 500151
Thread Size: 1-1/4" FPT (Female Pipe Thread)
Required Hole Size: 1-3/4" diameter
Fitting Style: Raised Spinweld
Material: Durable Plastic
Compatible Tanks: RV Fresh Water Tanks, RV Holding Tanks (polyethylene)
Installation Method: Spinweld (heat-spin bonded to tank wall)
Manufacturer: Custom Plastics (CPI)
Condition: New
Unit: Sold individually (Each)

What's Included

One (1) CPI 1-1/4" FPT Threaded Raised Spinweld Fitting — Part #54LL (500151)
30-day return policy

Compatible Models & Alternatives

Looking for a different size or style? Browse related CPI fittings: 1-1/4" FPT Flat Spinweld #55, 1-1/4" Spigot Spinweld #61, and 2" Raised Fitting #65M. Browse our full RV Tank Fittings collection for the complete CPI lineup.

Frequently Asked Questions

What hole size do I need to install the Part #54LL spinweld fitting?

The CPI Part #54LL requires a 1-3/4" diameter hole in your tank wall for proper installation.

What is the thread size on the 54LL fitting?

The fitting has 1-1/4" FPT (Female Pipe Thread), which accepts standard 1-1/4" MPT male pipe thread fittings and adapters.

What is the difference between a raised and flush spinweld fitting?

A raised spinweld fitting like the #54LL has an elevated boss above the tank wall, providing extra clearance for hose connections and easier wrench access. A flush fitting sits flat against the tank surface, which is better when space is extremely limited.

Is this fitting compatible with both fresh water and holding tanks?

Yes — the CPI Part #54LL is designed for use with both RV fresh water tanks and holding tanks (grey and black water) made from polyethylene.

How is a spinweld fitting installed?

Spinweld fittings are installed using a drill and spinweld tool that spins the fitting at high speed against the tank wall, generating friction heat that fuses the fitting permanently to the polyethylene tank. This creates a leak-resistant bond without adhesives or sealants.

Where can I buy the CPI Part #54LL spinweld fitting?

ElkhartRVParts.com is an authorized CPI dealer. Order directly here for guaranteed authentic OEM-grade parts with fast shipping.

Why Buy from Elkhart RV Parts?

As an authorized CPI (Custom Plastics) dealer, every fitting you purchase from us is 100% genuine OEM-grade. We stock authentic parts, ship fast, and back every order with our 30-day return policy. Our team specializes in RV plumbing — we're here to make sure you get the right part the first time.

Ready to order? Add the CPI Part #54LL to your cart today for fast shipping. Have a question about fitment or compatibility? Use our AI Live Chat for instant answers from our RV parts experts.

CPI Raised Fittings

CPI - 1-1/4" FPT Threaded Raised Spinweld Fitting - 1-3/4" Hole Size - Part # 54LL (500151)