Steam turbine and rotating blade

A blade mountable to a disc, the blade comprising:

• a blade platform;
• and
• a blade root extending from the blade platform, the blade root comprising first, second, and third hooks and first, second and third necks, wherein each hook comprises a contact surface and a non-contact surface, and an angle between each contact surface and each non-contact surface is about 70.6°.

A turbine, comprising:

• a blade comprising a blade root extending from a blade platform, the blade root comprising first, second, and third blade hooks and first, second and third blade necks, wherein each blade hook comprises a contact surface and a non-contact surface, and an angle between each contact surface and each non-contact surface;
• a rotor disc comprising a slot, the slot comprising first, second and third rotor hooks and first, second and third rotor necks, wherein each rotor hook comprises a contact surface in contact with a corresponding contact surface of the blade and a non-contact surface spaced from a corresponding non-contact surface of the blade, wherein the rotor contact surfaces are angled from the rotor non-contact surfaces at the same angle as the angle between the blade contact surfaces and the blade non-contact surfaces, and the angle is optimized to reduce local and average stresses between the contact surfaces.