3. Advanced reference systems

3.1 Tightening or favorable and unfavorable play

Schematically, a connection is clamping if the shaft is larger than the bore, with pressure and deformation distributed around the surface. The least-squares axes are assumed to coincide.

A loose connection is one in which the shaft is smaller than the bore. This clearance allows a small degree of mobility between the two parts. This clearance can be favorable for a single requirement and implicitly unfavorable for other requirements, as it is impossible to move the part in two different directions to meet two different requirements.