4-40 machine screws are fully threaded, this disqualifies them from be a good shear fastener. The threads would be the bearing surface during shear loads.
Shear loads are best met with smooth round and tight fitting fasteners. Machine screws do not fit that definition. While it may be true that the material of the screw may have a higher shear value than the rivet, the rivet is better designed to do the job.
Bob:
Have to take issue with your statement. The important consideration is joint geometry and the ability of the fastener to meet the needs of that geometry. Without knowing the joint design, load or fastener application, its pretty pointless to know the shear and tensile strength of like diameter fasteners. For example, in the fastening of wheels on heavy trucks, virtually all studs are threaded full length. While these fasteners have substantial shear strength, their function is to provide clamping force which in turn supports the load of the vehicle. If the clamp load is lost (loose nuts) and joint loading becomes shear, the studs will fracture and the wheel(s) will come off.
Typically, a joint utilizing torque or axial force on the fasteners is attempting to engage the geometry or friction of the mating surfaces to support the load. Think of the male fastener as a rubber band. The further it is stretched without breaking, the more clamp load it provides. This is why torque angle rather than torque loading (pound-feet) is the preferred method of maximizing clamp force. Angle, or linear distance up the thread helix, is a more accurate method of getting the desired stretch. Blind rivets also take advantage of a target clamping force by virtue of the load required to fracture the pin during setting. Shear strength of such fasteners is typically of secondary importance.
Terry
RV9A
N323TP
