Integral Drill Steels are normally produced from 19mm (3/4" ), 22mm ( 7/8") or 25mm (1") Hexagon Drill Steel, where the dimensions given are measured across the flat of the hexagon.
Integral Drill Steels are a fixed length with a shank at one end and a bit at the other, and are able to drill to a depth equivalent to their effective length. The bit may consist of a single chisel shaped tungsten carbide insert or three such inserts.
To drill deep holes, the rods are designed to be used in a series where the length of any rod used is longer than the one used just before it. To do this, a series of rods must be produced so that the bit diameter is reduced for each increase in length of rod to prevent jamming of the bit in the hole.