What's the spring for?

[Texas Jim]

Pardon my ignorance, but there is a spring in the bag that came with my S500. What is it for?

[Elwood]

Probably the third spring to increase the tremelo resistance,
Often when guitars are set up with light gauge strings , only two springs are used if a light touch on the tremelo is desired.
You can take the back cover off to see how many springs it has presently. Most folks use three, some use five (hendrix), but two will work if the screws in the spring claw are adjusted properly
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[Texas Jim]

Thanks for the info, I had no idea what it was for.