Extended means this has longer tooling. The failed hole or HeliCoil insert should not be larger than .660 inches or 16.8mm

M14x1.25 BIG-SERT Extended kit Includes 8 assorted length inserts (Qty 1) 51401 Washer seat 9.4mm (copper)/ (Qty 2) 51407 Washer seat 16.8mm (copper)/ (Qty 1) 51409 Washer seat 23mm (copper)/ (Qty 1) 51453 Taper seat 11mm (silver) /(Qty 2) 51457 Taper seat 16.8mm (silver)/ (Qty 1) 51469 Taper seat 24mm (silver)

" OVERSIZED HOLES" For Spark plugs that have been previously repaired.