a fastener with a tapered head that frictionally mates with a tapered hole in a punched sheet . frictional attachment is achieved with the fastener head remaining flush with the top of the panel . if a second panel of softer material is placed underneath against the backside of the first panel , in the same pressing step clinch features on the shank of the fastener attach to the second panel and attach the two sheets face - to - face . attachment of the tapered head with the top panel exploits two different attachment phenomena : a locking taper and , depending on the choice of materials such as stainless steel , attachment by galling .