Help with size of copper tubing and compression fitting

The Guide to Compression Fittings for Copper Pipe

Brass, For 1/4 in Tube OD, Male Connector - 1PZV9

Compression vs. Flared: When to Use Each Type for Brass

LTWFITTING 1/2 in. O.D. Brass Compression Coupling Fitting (20-Pack) HF62820 - The Home Depot

Brass, Metric x Compression, Brass Metric Compression Fitting - 791P86

How to Join Dissimilar Pipes

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The Basics of Compression Fittings - Beswick Engineering

A Guide To Pipe Fittings and How To Use Them

How to install a compression fitting on copper or plastic tubing - Quora

Everything You Need To Know About Copper Pipe Fittings