If you need a clamp of a certain size, it can be made from what is at hand: steel rod, strip, angle or profile. Making them need the bracket, drill holes in it and threaded (or welded nut) under the clamping bolt and the tool is ready.
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IF NO CLAMP
Support the work piece on the table, the workbench, impact glue sticks, drill the plate pack — in these and many other cases not to do without clamps, but not one, but several and...
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To shorten a long bolt or stud, such a task is not so rare encounter tinkerers. In order not to damage the grip of the thread, I suggest to use a simple tool, which is a metal strip 5-10...