In the LM Guide model number configuration example, the symbol "Y" is used only for Model SR and Model SSR. What does this symbol represent?｜Frequently asked questions (FAQ) about our products｜Product Information

In the LM Guide model number configuration example, the symbol "Y" is used only for Model SR and Model SSR. What does this symbol represent?: The symbol "Y" indicates different LM rail mounting hole dimensions.
Compatible model numbers are Model SR and Model SSR sizes 15 and 25.