HSS (High Speed Steel) drill bits used to drill holes in metal, hardwood or plastic window and door frames Long series to drill deeper holes, when drilling deeper holes, we recommend you clear the flute frequently to prevent over-heating. Long series HSS drill bits are stocked in thicknesses from 3mm to 10mm and lengths ranging from 100mm to 184mm to accommodate a wide range of fixing sizes. All drill bits are packed in 10’s.