A downhole stabilizer (5), such as a drill motor stabilizer, comprises at least one reaming means and/or reinforcing means (10). The present invention also relates to an assembly (30), such as a downhole drilling assembly (31), comprising at least one such stabilizer (5) and/or a drill bit (40,41) comprising a gauge bit (42) at or near a drilling end (45) thereof, and a connection means (46) for connecting the drill bit (40,41) to a drill motor assembly (60), wherein the drill bit gauge (42) comprises a substantially cylindrical portion having a length less than or equal to approximately 1.0 times the nominal bit diameter. The present invention also relates to a novel locking mechanism (80), such as a lock and key mechanism, to allow locking of a shaft (70′), e.g. a motor drive shaft (71′), through or together with a stabilizer (5′).