This frame is in great shape, the bike was not used much by the previous owner and doesn't have a lot of miles on it. It takes 650c wheels, and has a standard 1-1/8" head tube.

Other measurements:

51cm seat tube (c-t)

51cm top tube (c-c)

68mm bottom bracket shell

27.2mm seatlost diameter

There is a very shallow dent in the top tube, see photos 11 and 12. It's maybe 1mm deep or so and doesn't affect the structural integrity of the frame.

Feel free to message me with any additional questions.