A tolerance ring is a radially sprung ring that is press fitted between two mating components to act as a frictional fastener.[1] They are flexible shims designed to fix two cylindrical parts together.[2] The wavelike protrusions that run around the circumference of the ring generate a retention force to provide an optimal fit between the two mating components without the need for adhesive or excessive assembly force, simplifying the process for manufacturers.[3] They allow for any misalignment caused by thermal expansion or excessive vibration.[1] Tolerance rings can be used as bearing mounts and as a means of dealing with torque transfer, torque overload protection and axial slip between mating components.[1][4] They are often used to isolate undesirable vibration in engines and electric motors, for noise-free mechanism operation in passenger vehicles and domestic appliances, where noise reduction has become a major trend in recent years.[3][4] Modifications to tolerance rings can be made to tune the dynamic stiffness and, therefore, the frequencies that can be isolated.[4]
Tolerance rings can be used to eliminate noise completely, simply by taking up clearance between mating components, which could otherwise lead to rattling in the system as the parts are not completely constrained.[3]