Killua's yo-yos

Killua is in possession of two specifically designed Yo-Yos. He uses them as his weapons of choice. The yo-yos are extremely durable and heavy, each weighing 50 kilograms, due to their being made out of a special metal alloy.

Appearance
In the manga the yo-yos have a six point star or hexagram design on them. The hexagram design is used in many various religions and cultures including Islam, Christianity, Occultism, Hinduism and especially Judaism where the hexagram is the symbol used for "The Star of David". In theGreed Island OVAs the Hexagram or Six Point Star is changed into a Pentagram or a five point star. However, later in the Chimera Ant arc, Killua is seen using a yo-yo that has a pentagram on it. Since Killua has two yo-yos, it is most likely that one yo-yo has a hexagram while the other has a pentagram.