ISO INTERNATIONAL STANDARD 6696 First edition 1989-12-01 Cycles - : Screw threads used in bottom bracket assemblies Cycles - Filetages utilises dans les ensembles boites de pedalier Reference number ISO 6696 : 1989 (E) ISO6696:1989(E) Foreword Iso (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO miember bodies). The work of preparing International Standards is normally carried out through Iso technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison:with Iso, also take part in the work. iso collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISo Council. They are approved in accordance with ISO procedures requiring at least 75% approval bythe member bodies voting. International Standard ISO 6696 was prepared by Technical Committee iSO/TC 149, Cycles, ? ISO1989 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postate 56· CH-1211 Geneve 20·Switzerland Printed in Switzerlanid i Coovriaht Internafional Oraanization for Standlardization ISO 6696 : 1989 (E) Introduction Inch screw threads of British Standard Cycle (B.S.C.) thread profile are used exten- sively throughout the world for various applications on bicycle components, and have been standardized in national standards. The purpose of this document is to provide an International Standardforthe particular screwthreadused to assemblebottombracket cups to bottom brackets on bicycles: it is based on the use of the Iso basic thread pro- file and complies as far as is practicable with existing International Standards for general purpose screw threads. The change to an Iso system of screw threads will inevitably take a long time to com- plete in view of the millions of bicycles now in use which employ B.S.C. thread profile inch screw threads and for which replacement spare parts will be required. For this reason, in order to minimize changes in production methods during the change to the International Standard, and also to secure satisfactory interchangeability with the B.S.C. screw threads now used, the ISO screw thread in this International Standard has the same pitch as that of the 1,37 in × 24 t.p.i. B.S.C. screw thread it is intended to replace; this means that the pitch is in inch units (turns per inch or t.p.i.) but all other dimensions are specified in metric units. A 1 3/8 (1,375) in × 24 t.p.i screw thread of IS0 basic profile has been adopted in this International Standard.The basic pitch diameter of this thread differs byonly 0,003 mm from that of the 1,37 in × 24 t.p.i. B.S.C. thread, but, due to the smaller crest truncation of the Iso profile (see figure 1) interference may occur at the major diameter when an iso cup thread made towards its upper limit is assembled with:a B.S.C. shell thread made towards its lower limit on major diameter. The possibility of interference occurring in this manner is considered to be unlikely in practice because of the effect of the manufacturing tolerances (negative on the cup and positive on the shell)and the usual practice of using high-crested screwing taps. ii Coovriaht International Oraanization for Standardization