Don't waste your time with old crap. Get a brand new set from Clark.
http://www.awesomepowdercoat.c...hermostat_flaps.html
I put a set in my engine when I replaced my crappy Chinese shroud with a Cooled1 replica thing shroud. Couldn't be happier. Solved the overheating issues I had on long freeway and 5%< grade runs.
Per Gordon's post, Clark has the older bellows-style thermostats, but they're pricey because they're getting rare. On my Spyder, I couldn't use one because the exhaust is in the way, so I fabbed up a Triumph choke cable to operate the flaps manually
And +1 on ditching the OEM straight blade cheesehead screws I used SS pan head allens, spring washers, and locktite on mine.