Slotted oval countersunk head machine screw dimensions are shown in the following chart according to ASME B18.6.3 standard.
The oval countersunk head has a rounded top surface and a conical bearing surface with a head angle of approximately 82 deg.
For short lengths of 82 deg of head angle, machine screws have heads undercut to 70 % of normal side height to have greater length of thread on the screws.
Some important notes from the ASME B18.6.3:
- Thread dimensions for the No.0000, No.000 and No.00 sizes are also included in the standard.
- The general data about the head height, bearing surface, gaging of recess, slot, length, tolerance on length, length of thread, points, finish, workmanship and designation of machine screws are given in the standard.
Note 1: Dimensions in this calculator are in inches.
Note 2: Machine screws shall have a definite underhead fillet large enough to ensure that full fastener strength is achieved. For countersunk head screws, the radius of fillet shall be no greater than 40 % of the basic screw diameter.
Note 3: Not practical to gage.
Note 4: Screws with these length and shorter shall have undercut heads as shown in the figure.
Note 5: No tolerance given for gaging diameter. If the gaging diameter of the gage is differs from tabulated value, the protrusion will be affected accordingly and the proper protrusion value must be recalculated using the formulas given in the Appendix of ASME B18.6.3.
Note 6: 2nd row gives the dimensions of machine screw with undercut (U) head if applicable. See Note 4 for more information.