This restrictor plate is ONLY compatible with the newer Omron microswitch PCB assembly.
More older models of LS-56 have a WHITE restrictor plate, and are NOT compatible with this product.
If you never swapped out the PCB assembly in your LS model, then the model with white square restrictor plate should have the Panasonic microswitch.
If you have swapped the PCB assembly recently, Omron switches require this plate and not the white plate.
If you're looking to go full Seimitsu but need the smooth circular motion of Sanwa's GTY restrictor plate, you're in luck. The LS-56 Octagonal Restrictor Plate is compatible with the following Seimitsu joystick models: