Thanks Ralph, I had some headaches with Whitworth, during my misspent youth I was enamered with MGA's and rode a 69 Norton Atlas. With FSU lenses I guess it's a crap shoot. The reason I was asking, I hear people raving about the lenses and was lookind at an online store that sells filters and adapters and found an adapter to use the lenses on my Nikons, but it said it fit L39 and M39 lensesw and I thiught they were different.