BARRICADE PART - STEEL BOLT 3/8"-16x3". Car bolts are the most common type of bolt and have a shallow mushroom head that makes them self-locking. Barricade carries one size, 3/8" to 16, in 3". But what does it mean to be self-locking? Once installed, you can turn these car bolts from either side with just a single tool - an 11mm wrench or a 14mm wrench.