this is a license taken in presenting the drawings which indeed are presented pictorially and schematically for purposes of illustration only the general characteristics of the prior art pedestal mounted boom have already been described referring to fig1 and 2 the tubular section of the boom is shown having an upper or first plate 32 and having spaced therefrom a lower or second plate 34 the first plate is normally under tension causing it to bend downwardly so that the boom tries to assume the position shown in phantom lines in fig1 the lower plate is normally under compressive forces these forces are due as previously stated to the load which is externally applied as well as to the load due to the weight of the boom material in order to offset this latter load i have prestressed the boom it is of course known to prestress materials and there is no claim that prestressing of materials per se is the invention which i seek to disclose and claim herein accordingly for purposes of illustrating the preferred embodiment the method of prestressing will be taken to be known generally although to my knowledge it is not known in this art in order to effect the prestressing anchor plates are provided such as at 36 in fig3 and 4 these anchor plates are positioned most preferably proximate to the longitudinal ends of the boom this would be the right hand and.