You will know if they are metric while attempting to replace, as the fastener hole in the couch/sofa may seem a little too large and will not screw in properly. You could replace the leg U.S. standard 5/16" hanger bolt with a metric sized one...if you can locate one.
A more simpler option is to remove the 5/16" hanger bolt from the new replacement leg and replace it with a dowel screw (the same hole will work). Then, after predrilling a 1/4" hole in the couch frame 3/4" or more away from the original hole, simply screw in the replacement leg. When tightened up flush against the couch/chair frame, it will be strong.
This is how to remove any hanger bolt. Do one of the following.
Discard the hanger bolt as these 3 methods will permanently damage the machine screw threads.
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