If you have previously downloaded the strobe disc, the old one was designed using 33 RPM, so it was a bit off. The new strobe discs are exactly 33 1/3 RPM.
Download by Right-clicking the following PDF files, and print it out with a printer (set printer resolution to 300dpi or higher).
The spindle hole is exactly the same diameter as a standard paper-puncher.
60Hz, 33 1/3 and 45 RPM
50Hz, 33 1/3 and 45.1 RPM (note: 45rpm strobe disc in 50Hz does not exist because the exact number of strobe dots is not integer number)