5/8" (16mm) core. New big glass hole mandrels are used to make large holes in glass beads, rings and loops for scarves, sculptures or core formed vessels. The mandrels have a 5/32" (4mm) diam. x 10" (254mm) long shaft. The handle is thin enough to make quicker rotations and thick enough to make it difficult to bend.
Please use all lampworking tools with due caution.