I believe your metric-to-fraction conversions are incorrect. Most stovebolt brake systems use 1/4 inch steel tubing from the master cylinder, going to the front and rear, and 3/16 inch steel tubing to each wheel (not 3/8"). That would be approximately 6.3 MM tubing to the front and rear and 4.8 MM tubing side to side. The T fittings at the front and rear will have one 1/4" inverted flare opening, and two holes for 3/16" inverted flare fittings. Those would be easily available in the USA, but possibly very difficult to find in Italy. There are conversion fittings to adapt metric-size brake tubing to American Standard thread brake parts. The smaller-diameter brake lines will still carry plenty of fluid to allow your brake system to work properly. Good luck!
Jerry

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