To adjust / change the tension in Seimitsu, Sanwa Denshi and Hori joysticks a spring is used, which an "x" amount of coils

In Crown's joysticks, high density grommets are used made from silicon.  The most widely used grommet is the HST35, with the higher number the higher the resistance (tension)

Quick Link: https://tinyurl.com/HSTTG