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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.
| Thread size | 1-1/4 inch FPT |
|---|---|
| Hole size (inches) | 1.75 |
| Fitting type | Spinweld |
| Connection type | Threaded Raised |
| Application | RV Fresh Water and Holding Tanks |
| Manufacturer | Custom Plastics |
| Part number | 54 |
| Alternative part number | 500151 |
| Material | Plastic |
- What size is the threaded fitting? The fitting is 1-1/4 inches with FPT threads.
- What type of tanks is this fitting compatible with? This spinweld fitting is designed for RV fresh water and holding tanks.
- What is the hole size required for installation? The fitting requires a 1 3/4 inch hole size for installation.
- Who is the manufacturer of this fitting? The fitting is manufactured by Custom Plastics, part number 54 (500151).
- Is this product new or used? This product is new.
Factory-Fresh OEM Parts — the same brands installed in new RVs straight from Elkhart. Genuine, name-brand components made to order — never generic, never outdated. Sourced directly from the original RV manufacturers for perfect fit and factory-level quality.