New GM crankshaft reluctor ring.  This is the pickup for the crankshaft sensor.  This is for a 24x model (BLACK crankshaft sensor) system.  These are commonly oxidized as in the photo from storage.  These are factory installed for:

97-04 LS1/LS6 Corvette
98-02 LS1 Camaro
98-02 LS1 Firebird/Trans Am
04-06 LS1/LS2 GTO
99-05 5.3L/6.0L Trucks

NOTE : These will work in place of 58x systems when converting to 24x, or using a 58x crank in a 24x system.  These pickups are slight press fit to the crankshafts, and need to be aligned during installation.  There is a specific tool for installation, and these can be installed without a special tool if done properly.  If you mark your crankshaft with your old one installed, you can reinstall in the same position.  You must heat the ring to allow it to slide over the crank.  You may need to have your scanner do a crank relearn procedure.