you don't identify the nationality of the bike. If it is British from say approximately 1965 or earlier,then the threading is likely Whitworth. If some other nationality then I doesn't know. You are unlikely to find these at a hardware store.
I got a few from Larry Black a few years ago. You might try him or another bike shop with vintage goods.
Larry can be reached through: http://www.bike123.com/
I attempted to mount a pair of Bluemel's Club Special mudguards today, us
ing the wingnuts that came with the stays/other mounting hardware.The frame
upon which I had hoped to mount the fenders has threaded fender eyelets: G ipiemme dropouts on the fork, Paragon dropouts with brazed-on eyelets in the rear.The wingnuts/screws that came with the Bluemels do not fit the eye lets on the bike and I would like to replace the Bluemels hardware with som ething that'll work.What is the "standard" threading for fender eyelets? W ill I be able to find appropriate screws at a Local Bike Shop? Home Depot? auto parts store? Your spare parts bin? Matthew BowneBrooklyn, New York