This is an OEM Subaru reverse lock-out roll pin for the WRX or STI six-speed transmission. If you’ve lost your roll pin, or it’s so loose it falls out, this is for you. Part number 0519S*B in the diagram.
Quarter shown for scale and not included.
Fits all 2004-2021 Subaru STI, and manual-transmisson 2015-2021 WRX.