In sheet metal working, when forming shapes such as flanges and in automobile body working, in general, one uses dollies of various shapes on one side and a hammer or a slapper on the other.

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Шалязен (оправка-лопатка)
http://www.npc-krovlya.ru/upload/iblock/23c/b9b2c58d_5153_11...
http://www.npc-krovlya.ru/products/krovlya/komplektuyushchie...

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Dollies –Vital Tool Assisting Sheet Metal Forming Tasks
At Woodward Fab, we maintain a rich inventory of tools to carry out sheet metal forming activities safely, efficiently, and quickly. Generally, forming dollies are used in conjunction with hammers. The main purpose of the dolly is to support the work piece during metal shaping/forming operation
https://www.woodwardfab.com/wp-content/uploads/2014/11/handy...
https://whttps://www.woodwardfab.com/wp-content/uploads/2014...

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Our MetalAce Large Straight T-Dolly is used to form flanges and edges by hammering (with hammer or slapper) the metal over a rounded dolly.

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Dressing a flange with hammer and dolly on 18 gauge steel
https://www.youtube.com/watch?v=AlrPY-Ndo2c


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A 'dolly' is the name given to a category of tools used in shaping sheet metal. In general, a dolly is a solid piece of metal, small enough to hold in one hand, with a curved or shaped face. Generally a dolly will have more than one surface, each with its own radius of curvature (much like a three-dimensional French curve), allowing the craftsman more flexibility in using the tool.

https://en.wikipedia.org/wiki/Dolly_(tool)

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Dollies & Forming Heads
Dollies can be used for a variety of metalshaping and body repair operations. T-Dollies are used to form flanges and edges by hammering (with hammer or slapper) the metal over a rounded dolly. Forming heads can be treated like an anvil and are used for a variety of metal shaping projects. All of our selection is made in the USA.
http://www.trick-tools.com/Dollies_Forming_Heads_63?view_all