Mercury Quicksilver Fuel Line Connector 22-33821 | 1/4" NPT x 3/8" Inverted Flare Brass Fitting

OEM Brass Fuel Line Connector for Mercury & MerCruiser Fuel Systems

The Mercury Quicksilver 22-33821 is an OEM brass fuel-system adapter fitting that connects internal fuel lines to compatible fuel filter or water-separating fuel bracket assemblies on select Mercury and MerCruiser applications. Its 1/4" NPT male inlet and 3/8" inverted flare outlet provide a secure, leak-free transition between the fuel delivery line and the filter bracket port.

Brass construction makes this fitting resistant to fuel degradation and corrosion in a marine environment. It should be replaced any time it shows signs of leakage, thread damage, or corrosion — a compromised fuel fitting is a safety concern and should never be left in service.

Part Information

• Part Number: 22-33821
• Short Reference: 33821
• Brand: Mercury / Quicksilver
• Official Product Type: Fuel Line Connector / Adapter Fitting
• Barcode / UPC: 745061136892
• Material: Brass
• Thread Configuration: 1/4" NPT male inlet × 3/8" inverted flare outlet
• Approximate Dimensions: 1.0" L × 1.0" W × 1.0" H
• Approximate Weight: 0.03 kg (0.06 lb)

Compatible Applications

• Select Mercury and MerCruiser water-separating fuel filter bracket assemblies requiring a 1/4" NPT × 3/8" inverted flare connection
• MerCruiser Scorpion 377 / 6.2L V8 inboard fuel system applications where this fitting is shown in the parts diagram
• Any Mercury or MerCruiser fuel system application where the parts diagram specifies part 22-33821 or 33821 at the fuel line-to-bracket connection

Fitment Note: Verify by engine serial number, fuel filter bracket diagram, thread type, and original fitting part number before ordering. Fuel fittings vary by bracket style, fuel-line flare type, port size, and production range. Confirm both the NPT size and the flare type before ordering.

System & Diagram Position

This fitting is part of the fuel delivery system. In the Mercury parts diagram it appears in the fuel filter bracket or fuel line section, at the connection point between the incoming fuel line and the filter bracket inlet port. It bridges the NPT-threaded port on the bracket to the inverted flare fuel line, maintaining a sealed, pressure-rated fuel connection at that junction.

Dimensions

• Inlet Thread: 1/4" NPT male
• Outlet Connection: 3/8" inverted flare
• Approximate Overall Size: 1.0" × 1.0" × 1.0"

When to Replace

• Fuel seepage or dripping at the fitting connection
• Visible corrosion, pitting, or green oxidation on the brass body
• Cross-threaded, stripped, or rounded fitting that cannot be properly torqued
• Cracked or damaged flare seat that prevents a proper seal
• Any time the fuel filter bracket is replaced or the fuel line is disconnected at this fitting

Installation Notes

• Confirm both the NPT thread size and the inverted flare size match your application before installing
• Apply fuel-rated thread sealant (such as Teflon tape or liquid thread sealant) to the NPT threads only — never apply sealant to the inverted flare sealing surface
• Hand-tighten first, then torque to the specification in the Mercury service manual for fuel fittings
• Do not overtighten — brass fittings can crack or strip if over-torqued
• After installation, run the engine and inspect the fitting carefully for any fuel seepage before returning the vessel to service

Related Parts

• Mercury Fuel Pump Gasket 27-34213
• Mercury Quicksilver Exhaust Manifold Gasket 27-33395

Technical FAQ

Q: What is an inverted flare fitting?
A: An inverted flare fitting uses a cone-shaped seat that faces inward (inverted) to create a metal-to-metal seal with the flared end of the fuel line. It is a common fuel-system connection style in marine and automotive applications and requires a matching flare on the fuel line — it is not compatible with standard (SAE) flare or compression fittings.

Q: Can I use a generic brass NPT fitting instead?
A: Only if the thread sizes and flare configuration match exactly. The inverted flare outlet is a specific geometry — a standard NPT-to-barb or NPT-to-compression fitting will not seal correctly at the fuel line connection. Using the OEM part ensures the correct fit and a fuel-rated seal.

Q: Should I use thread sealant on this fitting?
A: Yes, on the NPT threads only. Use a fuel-compatible thread sealant (Teflon tape or liquid sealant rated for fuel systems). Never apply sealant to the inverted flare seating surface — the flare creates its own metal-to-metal seal and sealant on that surface can prevent proper seating.

Q: How do I know if this fitting is the right one for my fuel filter bracket?
A: Look up your engine model and serial number in the Mercury parts catalog and locate the fuel filter bracket section. If the diagram shows part 22-33821 at the fuel line inlet connection, this is the correct fitting.

Parts Desk Insights

Best use case: This fitting is the right call when replacing a leaking or damaged fuel line connector at the filter bracket on a compatible Mercury or MerCruiser fuel system. It is also the correct part to have on hand during any fuel filter bracket replacement where the existing fitting shows corrosion or thread wear.

Common mistakes: The most frequent mistake is ordering a generic brass NPT fitting without confirming the outlet connection type. NPT-to-barb and NPT-to-compression fittings look similar but will not seal correctly at an inverted flare fuel line. Always confirm both the NPT size and the flare type before ordering. A second common mistake is applying thread sealant to the flare seat — this prevents the metal-to-metal seal from seating properly and can cause a fuel leak at the flare connection.