M5-(0.90) Hex Nut Class 1 Former JIS 0.90 Pitch Trivalent White Cr-3 Thread pitch 0.90mm Pre ISO. These are the old Japanese Industrial Standard Type 1 Nut with the 0.90 pitch thread Used on older Pre 67 motorcycles, toys, European cars, drums and other musical instruments, models, telescopes, radios.
