Not just Wico joysticks - grommets were used in many joysticks.
Atari sticks..... Battlezone, Food Fight, Red Baron, etc.
But a grommet could also be considered the rubber "doughnut" that wires are fed through on say a metal panel to prevent chaffing the wires.
I'm not sure which "grommets" Ponyboy actually has...... never looked to be honest.
If he's calling them "centering Grommets", then they are joystick related.