What size of compression fitting do I need?

It is important to understand the difference between

PlumbShop Straight Compression Fittings, Chrome, 5/8-in OD x 3/8

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Brass Compression Fittings and Adaptors

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Brass Compression Fittings and Adaptors

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Full Size Hardware Brass Fitting Brass Compression Fitting Female

A Complete Guide to Compression Fittings

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Regusol Compression fitting for copper and precision steel pipe

Compression Fitting 101: Everything You Need to Know

How to Determine Pipe Thread Type and Pipe Size – Fresh Water Systems

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