This is LIKELY what you need.
0.121" / 3 mm long set screw for Push-In and Rail Tail tremolo systems. Note: These require a 2mm allen wrench to adjust.
www.floydrose.com
I'm assuming it fell out while you were working on the guitar and it got lost in the carpet. Use a flashlight and an old hairbrush to try and find it, or empty the bin on your vacuum cleaner and vacuum the area you dropped it, then fish the screw out of the dust bin.