Building your first custom loop is exciting, but nothing kills momentum like realizing halfway through assembly that you're missing a fitting. Compression fittings are the backbone of any loop and come in straight, 45-degree, and 90-degree rotary styles, so grab a mix before you start. Rotary fittings in particular are worth the extra cost since they let you adjust tube angles after everything is tightened down.

Stop fittings and drain valves are easy to skip on a first build, but you will be grateful for both the first time you need to bleed air or swap coolant. A handful of extension fittings also go a long way toward cleaning up awkward gaps between components.

Pick up a few extras of whatever thread size your blocks use. Fittings are inexpensive compared to the rest of your build, and having spares on hand means a stripped o-ring does not turn into a delayed weekend project.