The balu is the wooden mallet used to strike the agung or large gongs. The mallets are commonly short and made of hardwood while the striking end has a rubber of padded material that can strike the brass agung without damaging both materials.
This balu (image above) is carved wood with metal sheets wrapped at the handle while the other end has a cloth wrapped around the striking end. The balu can come in many forms and does not necessarily need to be decorated. However, a decorated item carries more prestige.
You may want to read: