A top jaw and insert for use in connection with chucks of turning machines, or latches, are disclosed. Each insert is held in a recess in a top jaw and precisely positioned relative to said top jaw by: the outer end portion of the sidewalls forming the recess are precisely machined to provide parallel sidewall surfaces; additional mounting surfaces are provided on the opposite end portions of said sidewalls and located normal to the sidewall surfaces; an insert is provided with sidewalls to slidingly fit into said recess; the insert is provided with a head of a size to arrest further movement therepast of the insert into the recess; a machined under surface is provided on said head to mate with the surfaces at the end of the sidewalls; and set screws are threadingly mounted into said sidewalls, engage grooves in the insert, and upon rotation thereof, the set screws urge the insert and the machined surface thereof, on the underside of the head thereof, against the base surfaces and on the sidewall. Also, each of the sidewalls of the top jaws has mounting surfaces at each end portion thereof so that the insert can be carried by either end portion of the sidewall and carried by the top jaw.