Glue brushes come in a variety of sizes. I usually buy very cheap package brushes from Dollar General or, the ones I prefer, a big pack of artists brushes from Michael's or Hobby Lobby. Those work for general glue work like tip-ins, re-backs, etc. For bigger work with fabric, like re-casing a book, I like to use a stiff glue brush like the one found in Gaylord's. Whatever your choice, always remember to wash the brush out in soapy water and allow to dry after use.