You have the right mirror.There is no actual thread on the shaft of the mirror this is so you can swivel it to your preffered position.I can only assume you need the clamping assy also.Basically a Male/Male adapter one end (looks about M10 poss fine)Screws into the bracket on the handle bar.The other end has a larger thread on it(M14?fine?)a hole for the mirror shaft and a taper on the end with four slots cut in its length its nut has a coresponding taper which when you tighten the nut clamps the mirror shaft.The whole lot has a pretty rubber cover over it to hide it all!
Hhmmmmmmmmmm............ i reckon i could have explained that better!