NGK #4006 14mm Long-Reach (3/4") Spark Plugs, Pack/4, Type 4

Some aftermarket Type 1 heads, and even some of the VW factory heads (such as those manufactured in Mexico), came with longer reach (3/4") spark plugs that have the stock 14mm hole diameter in them.  All Type 4 engines also utilize this design.  Knowing that the 1/2" reach spark plug threads tended to strip easily and crack at the threads, this design helped strengthen the original design.  This is the spark plug to use for these applications.