Priced Individually TIME-SERT 51457 14x1.25 Tapered Seat Over Size Steel Insert with 16.8mm reach - considered 3/4" reach. 51457 is fully threaded, unlike the 51459. It is made for spark plugs that have threads on the length of the plug that sits in the insert.  *Note, requires the 51484A to be used on setting tool or thread damage may occur when installing. 

BIG-SERT TAPER SEAT INSERTS FOR FULLY THREADED SPARK PLUGS.

*Loctite sealer is required for ALL taper seat inserts. Use of PN 6020 is recommended.

Question - Why is there a chunk missing out of the side of the insert?

Answer - The piece missing is NOT a defect. Time-Sert calls this part of the insert the "socket with metal locking pin". It is an engineered locking design. Once the insert is installed with the driver, the locking pin is pushed out and locks the insert into place. This creates a "cam lock" which helps to insure the insert will NOT back out.