126 contained within an adjustable yoke 128 the yoke 128 extends within an internal annular aperture 130 formed in the horn member 120 a bolt 132 which has an irremovable rotatable retention washer 134 secured about its shank adjacent the head thereof is threaded within an internal aperture in the top of the adjustable yoke 128 the retention washer 134 is slightly larger in outer diameter than the internal angular aperture 130 and is bottomed against a land 135 in an enlarged annular aperture 136 formed coaxially with the annular aperture 130 a cap member 138 overlying the retention washer 134 retains the retention washer and bolt 132 securely in place the cap member 138 is secured to the horn member 120 by a plurality of bolts 140 therefore the adjustable yoke 128 may be raised and lowered by simply turning the bolt 132 the lower lock seaming roll 124 is composed of a roller 142 which complements the shape of the roller 126 and which is mounted within a slidable yoke 144 the yoke 144 has a lower carriage portion 146 having flanges 147 which are positioned about a flanged rail 148 securely attached to the table 76 by a plurality of screws 150 the position of the.