Skil 10 Pc. Forstner Wood Boring Bit Set with Wooden Box 3/8 in. shank size, 10 pieces. forstner bit set and wooden storage box Sizes are 1/4, 3/8, 1/2, 5/8, 3/4, 7/8, 1, 1-1/4, 1-3/8 and 1-1/2 in. For boring sides and flat holes. Uses drill presses and drills with 3/8 in, 1/2 in. chucks.