F/F4 Series Self-Clinching Flush Fasteners PEM F/F4 Series Self-Clinching Flush Fasteners are fasteners designed to be installed into stainless steel sheets as thin as 1.5mm. The fasteners' hexagonal head with the self-clinching design ensures high axial and torsional strength. PEM F/F4 Series Self-Clinching Flush Fasteners are ideal for applications enhancing the functional and aesthetic qualities of the assembly with no protrusions.