Joined: Jan 2009
Posts: 44,222
Likes: 6,476
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
There's a good chance it's Swiss-threaded.
First of all, why change the crank?
Secondly, if you have to change the crank, you may not have to change the bottom bracket. So don't worry.
Thirdly, if you have to change the bottom bracket, there are threadless designs so you don't have to find a Swiss-threaded one.
Tom