FOREWORD (a) These specifications@ for pumping@ cable tool@ and rotary drilling rigs and derricks were prepared by the A. P. I. Committee on the Standardization of Standard Rigs and Derricks and are recommended for the use of the oil industry in all districts of the United States. (b) This Committee@ which is composed of representatives from all districts@ first collected and tabulated various dimensions of derricks and standard rigs used throughout the industry@ A process of consolidating similar dimensions resulted in the elimination of a great many different height and base sizes. (c) Derrick and Standard Rig manufacturers have been represented at all meetings of this Committee@ so that the industry as a whole@ including manufacturers as well as users@ has aided in this standardization work. (d) Effective Date: Authority to use the A. P. I. monogram on standard rigs and derricks will be granted to manufacturers 90 days after the final publication of the first edition of these specifications@ upon their making application therefor in the form presented in the Appendix. (e) Revisions: These specifications will be in effect for one year following date of publication@ after which they can be revised by regular Committee action@ except that@ in order to care for changes which may prove necessary on account of obvious errors or inconsistencies@ upon approval by the Engineering Sub-Committee@ the matter may be referred at once by letter to the membership of the various Committees that have been active in drawing the specifications@ and a letter ballot taken on the proposed change@ which may then be made effective at once.