The most common positive-drive assembly is the conventional key/keyway system. Other positive drive assemblies involve the use of grub screws, pins and spline shafts.
They transmit torque levels commensurate with the degree of mechanical interlocking achieved.
These assemblies (except the spline shaft) have an uneven distribution of mass, an imbalance that can lead to vibration at high speeds. All positive drive assemblies allow micro-movements. This results in wear and tear (e.g. in the form of fretting corrosion), with the risk of development into macro-movement failures, particularly in dynamically loaded assemblies.
- High stress concentration due to the "notch effect" that occures in the area of a key. Also permanent relative movements lead to abrasive wear of both parts e.g. key and shaft.
- Uneven distribution of mass.