
You will know if they are metric while attempting to replace, as the fastener hole in the couch/sofa will seem a little too large and will not screw in properly. You could replace our U.S. standard 5/16" hanger bolts with a metric size...if you can locate one.
An simple option is to remove the 5/16" hanger bolt from the new replacement leg and replace with a dowel screw
. Then, after predrilling a 3/16" 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, first do one of the following.