The thread dimensions and profile accuracy are crucial for determining:
- Whether a coating can still be applied to the screw thread
- Whether the parts to be joined can be screwed together on assembly without difficulty or the need for reworking
- Whether the thread can transmit the forces for which the components were dimensioned.
Tolerances are very small in screw manufacturing. Terms and fitting systems are difficult to understand. To assist, the following illustrations explain dimensions and tolerances.
|Basic concept and nominal dimensions|
|Clearance fit on metric ISO threads|
|Tolerance fields for commercial screws and nuts*|
|Limits for metric (standard) coarse threads|
|Selection series for coarse threads|
|Limits for metric fine threads|
|Selection series for fine threads|
|Permissible tolerances for plastic fasteners|
*Available as PDF download for registered users.