He's talking about I-beam floor joists, ie. TJIs (from Trus Joist), BCIs (from Boise Cascade), LPIs (from Louisiana-Pacific), etc. Any lumber store that sells them should be able to provide you with an installation guide/flyer that has a hole chart showing what size and where holes many be drilled. Just be sure the hole chart is published by the manufacturer of the particular joists you are drilling. I try to keep one from each of the manufacturers in my office so that I can refer to the correct one.
