Jan 25, 2021 Jaw Crusher Parameters. Stroke (LT) Minimum and maximum movability of the lower end of the jaw. This is equal to the OSS minus the CSS. R: Size reduction ratio. The ratio of the gape width to the near side jaw opening. This ratio may vary from 1/3 to 1/9, but is generally 1/3 for primary crushers and 1/4 for secondary crushers.