This is a A-21A864 Autolite Spark Plug PN: 21A864Main Description As Following : A-21A864 Autolite Spark Plug P.N: 21A864 Dim A (1): Autolite 3116Quantity: 4Replaces: Champion D15YThread: 18mm Replaces: A-D15Y MISCELLANEOUS , A-207000684 WHITE TRACTOR , A-21A815 IH , A-360942R1 IH , Crossed From: M8AC0 BOSCH , 20-7000684 WHITE/ OLIVER/ MPL MOLINE , 5612080 GMC HOUSINGS Found in Section & Models : Ignition & Electrical Parts > Engine Related Parts, Case-IH TRACTOR: SEVERAL Associated Items : New Also A-MNL18344 And : Dim A (1): Autolite 3116 Quantity: 4 Replaces: Champion D15Y Thread: 18mm