outer shoulder 72 and inner shoulder 74 is just slightly greater than the combined width of lower end 26 and spacer ring 68 hence when the compound rivet 28 has been compressed so that head 58 locks housing bar lower end 52 in the recess 60 and side rail central web 56 and reinforcement member 76 are locked between button 66 and inner shoulder 74 the lower end 26 can freely pivot in the barrel portion 62 this mounting arrangement for the mounting bars 10 and hook locks 8 create multi directional strength for these units of the fly section 6 while still allowing wide movement for the hook locks 8 also the spacer rings 68 give lateral support to the hook locks 8 while providing that the hook locks clear the side rails 12 of the bed section 4 as they pivot in the space between the mounting bars 10 and the side rails 18 and 20 of the fly section 6 the step member 78 is fixed between the central web portions 48 of the housing bars 10 transversely of the side rails 18 and 20 of the fly section 6 with the spacing between step member 78 and other step members 22 of fly section 6 in conformance with the spacing of step members 14 of the bed section 4 the step member 78 is preferrably fixed to the central web portion 48 to be expanded portions 80 and 82 but any other suitable method of fixing the step member 78 on mounting bars 10 may be used the use of an extension ladder of the invention follows the.