This is a machined groove along the length shrinking dolly. This is the most effect way to cold shrink , the metal is driven into the groove and  the postion of the grove and the groves length determined be the area need to shrink. A stretch in one direction only can be remedied by the constuction of one rib at right angles to the direction of the stretch. To reduce a bulge: and X rib may be the best solution. For best succes you will need to dress a panel beater head to fit closely to the shrinking die groove or multiple grooves placed in X pattern. This dolly is also effective on welded joints when the welds and the weld is forced into the groove, weld will not be affected and it makes it somewhat easier to fill the groove and weld with a suitable body filler. 4 5/8" overall length, 3 lbs, 1" thick with a 12" radius on grooved side square bottom surface.

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