This is somewhat 'constructed' from the info you gave, not nedessarily a correct translation - I'd need to see a picture of the critter the provide that. However, I'm positive that the "shear pin' you mention is "brytepinne", a bolt that is being sheared if the torque on the drive exceeds a certain limit. The "square drive" might need a different term, but "firkantet drivaksel" does describe what it is...