Sitting here on this ex-milking stool ( repaired ) I was horrified to see some Gentleman holding a Cylinder Head by the Spark Plug hole. Now if this thread strips there is major expense ahead , so this was made out of bits of scrap. The holes in the Cylinder head were used to " spot through " drilled and tapped .It is important that the holes are drilled vertical and parallel , otherwise they will not enter the head holes.No dimensions are given since it depends on what scrap , " sorry " stock you have.