The handle opening dimension (outer dimension) is designed to be 150mm when the hole is 1m deep, so the handle can be used to dig without contacting the walls of the hole. This involves digging small, deep holes to collect soil samples from a depth of approximately 1 meter below the surface for soil investigation purposes. For soil investigation, a core drill of around 150 mm is used to dig holes in the floor to a depth of approximately 20-30 cm, and soil samples are collected from below.