Socketing
From Istaria Lexica
Socketing allows you to add a socket for crystals onto a tool, weapon, or armor item. Sockets are applied post-creation by drag and drop, similar to technique kits. Tier 1 and 2 items may have one socket applied, Tier 3 and 4 may have two, Tier 5 may have three while tier 6 items may only contain two.
You can apply those technique kits post-creation, or scribe them so you can use it on formulas.
Be warned! Do NOT socket your TOOL claw with Claw Socketing. Use Tool Socketing!
For more details about each of the techniques (e.g. where to buy), visit their article pages.