How normal is the gap between the inner tubes of coring bit?

1.5 to 2 cm. The spacing is the distance between the bottom of the core claw and the shoulder of the drill bit. By adjusting the ring, the spacing cannot be zero, otherwise the cycle cannot be realized. The inner tube gap of coring bit 1.5 ~ 2cm is normal, and circulation can be realized. Core bits are mainly used to drill holes in steel plates and other products, and hollow bits are used in conjunction with machines specially used for core bits.