fer·rule 
(fĕrəl)
(fĕrəl)n.
1. A metal ring or cap placed around a pole or shaft for reinforcement or to prevent splitting.
2. A bushing used to secure a pipe joint.
[Alteration (influenced by Latin ferrum, iron) of Middle English verrele, from Old French virole, from Latin viriola, little bracelet, diminutive of viriae, bracelets; see wei- in the Appendix of Indo-European roots.]
ferrule v.
ferruletop to bottom: household paintbrush, round paintbrush, and cosmetic brush