Penn Engineering PEM® self-clinching press-in fasteners are a useful product for all sort of mechanical attachment to sheet metal, in particular for threads in sheet metal too thin to tap. The CL series nuts are the most common and provide good threads in all common sheet metal applications. Penn also makes all sort of threaded studs, threaded standoffs, alignment pins and such, most of which are set flush leaving a smooth surface opposite the business end.
The most common PEMs can be used in steel and aluminum. We tend to stock the stainless e.g. CLS- series nuts and not the steel nuts, because the cost difference is inconsequential and the stainless parts are useful in the widest variety of applications. Beware special high-hardness SP, SO4, BSO4, FH4 etc. series PEMs are required to insert into stainless sheet, see Bulletin SS below.
Following are embedded PDFs of the Penn Engineering / PEM® catalogs referenced by the above.
CL* self-clinching nuts: https://www.pemnet.com/fastening_products/pdf/cldata.pdf
SO* threaded standoffs: https://www.pemnet.com/fastening_products/pdf/sodata.pdf
FH* threaded studs and pins: https://www.pemnet.com/fastening_products/pdf/fhdata.pdf
SS* hardened fasteners for stainless sheet: https://www.pemnet.com/fastening_products/pdf/ssdata.pdf