Across flats and hex

When we design a special screw we must keep in mind that the distance across the flats should be based on standard end wrench (standard bolts and nuts sizes). If we choose larger size we risk over tighten the bolt and break it. At the figure above the hex distance of the pivot shaft is 14mm based on the bolt size M8. In detail A the 30° chamfer has specific dimensions: the size of the chamfer’s circle equals the hex distance (Ø14mm). This detail gives better appearance to the part.

At the figure above there are two more special screws (pivot shafts) with a build-in washer. You can see that the distance across the flats (and the hex distance) is based on the standard sizes for M8 bolt (the height of the feature is not). These parts are made from round stock. The round stock size must be minimum 1.155xHEX distance in order to have the prescribed circle of the hex feature smaller or equal the part’s external diameter. You can see how the part appears when you apply this detail at the below figure. Again on a special screw (rod-end screw and distance piece) there is a M8 bolt and a hex feature with 14mm distance. At both sides of the hex feature two Ø14x1mm shoulder provide a perfect blend between the screw’s ends and the hex feature. See how beautiful the chamfer blends with the shoulder diameter. The part at the figure below was made from standard hex bar.