Flats commonly required on typical machined parts are shown in Drawing #17.
Like slots, flats are milled on the part using one or more circular saws, or produced by broaching. Milling may produce a radius at A and if this can be allowed, a note stating this should be on the drawing as in Figure 1.
But, if a radius is not acceptable at A and a straight flat surface perpendicular to the flat is required at A, a note should be placed on the drawing. Cross milling or broaching is then used to produce both flat surfaces.
When the relationship between the flat to another surface on the part is important, it should be stated on the drawing and dimensioned so it can be measured.
When locating a flat on a cylindrical surface the use of dimension C as shown in Figure 1 is recommended.