VW CV joint bolt. These CV bolts are found on 1993-1999.5 Golf, Jetta, and Passat with 4-cylinder engines and automatic transmissions. After 1992 VW moved to various inner CV joint designs depending on your vehicle, engine, and transmission combination. There is also a longer version of these same bolts (#12355) for cars equipped with the wide flat inner joints more commonly found in all earlier cars (1977-1992), and manual transmission cars (1993-1999). After 1999 a 10mm short (#22417) and long version (#22418) were also introduced. If you are unsure of which size bolt you need it may be best for you to go and take one off your car and measure before you order.
If you're removing your driveshaft, you'll need an 8mm 12 point Allen star tool for the inner bolts, and the 30mm axle nut socket for the outer bolt. New axle nuts can be ordered as part #19931.