The introduction provides an overview of beginning the development of a plastic design of metal thin-walled cross-sections. This large study investigates in detail together 14 steel and four extruded aluminium cross-sections. Six groups of various shaped cross-sections that consist of: four I-shaped doubly symmetric sections (two I-sections, one I-section with lips, one H-section); three monosymmetric sections with axis of symmetry z (monosymmetric I-section, T-section, diamond section); four monosymmetric sections with axis of symmetry y (two channels, channel with inside lips, channel with outside lips); two point symmetric sections (Z-section with and without lips); four asymmetric sections (L-profile, sigma section, two closed sections: oblique and irregular sections; non-warping sections along midline, but with negligible warping along the element's thicknesses: Tsection and L-profile are included in the above groups. Four extruded aluminium cross-sections are: I 200a section, diamond section and closed oblique and irregular sections. For all 18 cross-sections, the plastic section moduli of three kinds were calculated: Wpl,y,nB, Wpl,z,nB for bimoment not considered to be constraint; Wpl,y, Wpl,z, Wpl,wfor bimoment considered to be restraint; maximum values Wpl,y,max, Wpl,z,max, Wpl,w,max. The values of cross-section plastic resistances Npl, Mpl,y,Rd, Mpl,z,Rd and Bpl are also calculated in numerical examples. The values of cross-section properties are calculated in different ways to verify the correctness of the results. The following ways of calculations are used: the rules in Eurocode EN 1993-1-1: 2022; own MathCad programmes; own software. Recommendations for educational institutes and designers in practice are provided, including simple formulae for all the cross-sectional properties for the doubly and monosymmetric I-shaped sections, channels and Z-sections. Formulae are presented in six tables containing formulae in the dimensionless form, which are useful for parametrical studies and formulae for direct designs. The background of the Eurocode rules in EN 1993-1-1: 2022 is explained together with recommendations about how to avoid problems with using them.