"FOREWORD (a) These specifications were prepared by the Special A. P. I. Committee on the Standardization of Rotary Drilling Equipment@ and are the result of extensive investigations embracing a period of over three years. Comprehensive field teats were made on various types before finally deciding on the joints specified herein. (b) The 5 x 6 ?? 4 and 4? x 5? ?? 4 joints were originally designed by the Union Tool Company. Torrance. California@ and have been in actual use for many years in all the oil fields of the United States and abroad. The gage dimensions shown in Table 2 were based upon pitch diameters one inch from gage step of 5.69530"" and 5.14027"" respectively@ furnished by the Union Tool Company. (c) The 7 x 8 ??4 joint was designed by the E. M. Smith Company@ Loa Angeles@ California@ and has been in actual service for a considerable length of time@ for use with 85/8"" O. D. or similar sized drill pipe. The dimensions shown in Table 2 were based upon radial measurements of pitch diameter over wire@ 0.200"" diameter@ at 5/8"" step@ equal to 4.0256""@ furnished by the E. M. Smith Company. (d) It should be noted that the American Petroleum Institute has not officially adopted any drill pipe larger in size than 6 5/8"" O. D. However@ due to the occasional use of 8 5/8"" and similar sized drill pipe@ it was considered desirable to set up a standard taper joint for use therewith. It should be borne in mind@ therefore@ that variations may exist in the pipe ends of rotary tool joints in this size@ and the purchaser should specify the size and threads desired to fit his drill pipe In the 8 5/8"" O D. or similar sizes. (e) The other sizes of taper joints contained herein are new@ and were developed by the Committee. These other sizes@ however@ so closely approximate sizes and threads now in general use@ that specific field tests were considered@ unnecessary. The dimensions given in Table 2 on the first 4 sizes were based upon Diameter ""A"" at small end@ as given in Table 1. (f) In all cases in computing thread height and truncation@ account has been taken of the effect of taper in reducing thread height for a given pitch@ as compared with values for the same pitch on a cylinder. (g) The thread specified herein conforms to the National Form of Thread@ except as to truncation of crests and roots@ which is definitely specified. (h) Particular attention is directed to the method adopted herein for identifying Rotary Drilling Taper Joints@ viz: the taper joint is known by the size drill pipe with which tool joints must be used. For example the 5 x 6 ??4 rotary tool joint is used with 6 5/8"" drill pipe and will be identified and marked as 6 5/8"" joint. In order to identify the joints in the tables of drill collars@ fishtail bits@ couplings@ etc@ the size drill pipe is listed with the nominal size of taper joint. However@ this does not prevent the taper joints@ being used in any combination desired for drill collars and fishtail bits."