They're for cable.There's a good picture w/cable on this page:

Cable Crimp Sleeves: What Are They and How Do You Use Them? | Sava
Cable crimp sleeves are a type of electrical connector that is used to join two or more wires together. They are available in a variety of sizes and materials, and they can be used for a variety of applications. This article provides an overview of cable crimp sleeves, including their different types, applications, and benefits.

(www.savacable.com)