"FOREWORD (a) These specifications were prepared by the A. P. I. committee on the Standardization of Rotary Drilling Equipment. (b) Included herein are complete dimensional standards for eight sizes of ""regular"" and five sizes of ""full-hole"" rotary drilling taper joints@ prepared after intensive investigations and filed trials. These joints are indentified as to ""size"" by the size of the drill pipe on which used. For example the outer (drill pipe) ends of the ""regular"" rotary taper joint having nominal pin dimensions of 5""x6"" ?C 4@ and of the ""full-hole"" joint having nominal pin dimensions of 51/1 5/6""x63/4"" -4@ are both threaded to fit 6 5/8"" A. P. I. standard internal-upset drill pipe@ and are therefore known as ""65/8-inch"" rotary taper joints. The letters ""FH"" are used to identify the full-hole tool joints. These specifications also include certain ""recommended practices"" in measurement (Section XIII) previously published in A. P. I. Stds. 7-A (now discontinued)@ and@ finally@ include new material previously published in Supplement No. 3 to the 5th Edition of Stds. 7-B@ this including standard center distance on rotary tables (Sec. XI) and brake bands and blocks (Sec. XII). "