The Quartz Fiber

The quartz fiber is used to share power between networks, while keeping them separate. This allows you to power subnetworks without needing to put energy acceptors and power cables everywhere. It can also be used to keep cables from connecting, although using cables of differing colors, or using Cable Anchor is cheaper and more effective.

They are cable subparts.

Recipe

Crafting
Minecraft 1.21 [change]