Metric Bubble To 3/16 Brake Line Adapter Fitting

Brake Line Adapter Fitting - 10mm x 1.0 Metric Bubble Flare to 3/16" Inverted Flare

Bridge the gap between European and American braking components with the Metric Bubble Flare to 3/16" Inverted Flare Adapter from Appletree Auto. This specialized fitting is a must-have for Volkswagen owners who are upgrading their hydraulic systems with American-style master cylinders, staging brakes, or line locks. It features a male 10mm x 1.0 bubble flare on one end (standard for VW) and a female 3/8-24 inverted flare seat on the other, allowing you to connect a standard 3/16" American brake line directly to your metric VW ports without flaring new lines.

Constructed from high-strength materials to withstand extreme hydraulic pressures, this adapter ensures a secure and leak-free connection. It is the perfect solution for custom Dune Buggy and Sand Rail builders who need to integrate various brake components into a single, reliable system. Whether you are plumbing a high-performance disc brake conversion or simply replacing a master cylinder, Appletree Auto provides the precision-engineered fittings required to keep your braking system safe and responsive.

Product Fitment & Compatibility

This adapter is designed for vehicles utilizing M10x1.0 metric bubble flare ports, commonly found on air-cooled Volkswagen models, and adapts them to 3/16" SAE inverted flare lines.

• Volkswagen Beetle (Standard & Super): All Years (Equipped with M10x1.0 metric ports)
• Volkswagen Karmann Ghia: 1956 - 1974
• Volkswagen Bus / Transporter (Type 2): 1950 - 1979
• Volkswagen Thing (Type 181): 1973 - 1974
• Volkswagen Type 3 (Squareback/Fastback/Notchback): 1961 - 1973
• Custom Sand Rails & Dune Buggies: All years utilizing VW-style metric master cylinders or wheel cylinders

Tech Tips & Installation Advice

• Identify the Flare Style: It is critical to recognize that this fitting joins two different sealing technologies. The 10mm side is a Bubble Flare (European style), and the 3/16" side is an Inverted Flare (American style). Ensure your lines and ports match these styles before installation to prevent cross-contamination of flare seats.
• Clean Seating: Before threading the adapter into your master cylinder or brake line, ensure all surfaces are free of grit and metal shavings. Since these fittings rely on a metal-on-metal seal, even a small piece of debris can cause a high-pressure leak.
• No Thread Tape: Do not use Teflon tape or liquid pipe sealant on these threads. The seal is created by the compression of the flare against the seat, not by the threads themselves. Sealant can actually get into the hydraulic system and cause valve failure or prevent the flare from seating correctly.
• Check for "Bottoming Out": When installing the adapter into a port, ensure it seats fully against the internal flare before the hex head hits the body of the component. If the fitting bottoms out early, it will not seal properly regardless of how much torque is applied.
• Safety Bleeding: Any time a brake connection is opened, air is introduced into the system. You must perform a full brake bleeding procedure, starting at the wheel furthest from the master cylinder, to ensure a firm pedal and maximum stopping power.