This wine stopper knob is made up of several individual strands interwoven together. It has some flex, but is quite sturdy! The stopper screws into a 3/8" hole with 16 TPI threads (TPI = threads per inch). The stopper pictured is from Niles Bottle Stoppers
, item number D-304 (make sure to specify 3/8" hole with 16 TPI). The metal designs require the threads to be chased in order to fit the stopper.