Needle set screw, holds the needles in.
Very small and hard to find part.
Fits these makes and models of Sergers:
Brother 546, 546D, 626D, 634D, 834DP Serger
Pfaff 774, 783 Serger
Viking 905, 910 Serger
Limited stock max per order of 4 screws.
Alternate Part Numbers Include 10141, 016300422