Thread Reliefs

  1. Edge distance rule of thumb: Allow 3 times a single thread height (1 pitch x 3) plus 1/2 the max thread diameter. This will be the distance from the centerline of the hole to the edge of the part. For example, the edge distance for a 4(.112)-40 screw would be (1/40*3)+(0.112/2)=.131 or a .262 diameter boss. If you are using a helicoil or keensert or would like to leave room for possibly adding them later, use the max diameter of the insert instead.
  2. In the table below:
Thread relief dimensions for tapped holes and threaded shafts (pdf)
plug end tap, bottoming tap and other thread reliefs