Usually a threaded hole isn't good design practice. As was stated, an open hole has a Kt of 3 and for a hole with a fastener, the Kt can go much higher (see Michael C.Y. Niu's books for stress at a loaded hole. Such as "Airframe Structural Design"). A threaded hole would probably have an even...
For a beam on two supports, I have developed a spreadsheet that calculates the shear, moment and deflections for various loadings (Point Load, Point Moment, or Linear varying distributed load) with end restraints of simple, fixed, cantilever beam, or...
