Fingertip fastener (4)
I believe the answer is:
nail
I believe this is a double definition.
'fingertip' is the first definition.
(I've seen this in another clue)
'fastener' is the second definition.
(I know that nail is a type of fastener)
(Other definitions for nail that I've seen before include "Hammered pin" , "Hammered individual" , "Metal pin, hit it on the head" , "Catch - fastener" , "Finger end; fasten" .)