A tombstone is a tall, multi-sided fixture block mounted on a horizontal machining center's rotary pallet. Parts are clamped on each face, so one rotary pallet can present many parts (or many faces of one part) to the spindle — dramatically raising the number of parts machined per setup.
Tombstones turn an HMC into a high-volume producer and are a big reason horizontals dominate production work.
Get a real number from a Machine Blue Book specialist — free, no obligation.