There are various drill bits for Mole, which are each designed for very specific soil properties:
Clay and damp soil
With narrow side panels for minimum soil friction/resistance. As wet soils are usually very cohesive, the soil still adheres to the bit very well.
Sand
With broad side panels and therefore a large retention capacity for the sand.
Coarse sand
With extra broad side panels enclosing even more of the bit so that even coarse sandy soils and very dry soils are retained.
Combination
Retains both strongly cohesive and less cohesive soils.
Riverside
Very suitable for drilling in hard, encrusted soils and soils mixed with fine gravel. The drill cutters project from the drill itself, so that friction is greatly reduced.
Gravel drill
With slightly rounded, oblique scoops which pull themselves downward in the gravel. Any stones present are clamped between the drill sides. Finer soil material (coarse sand with fine gravel) is retained in the drill bit.
Stone catcher
The stone catcher is used to collect and remove stones that prevent proper sampling with one of the other drill bits.