Bolts and nuts with small 12 pt heads are sometimes used in high
performance applications where limited clearance prohibits use of the
larger 6 pt heads. They aren't splined, but are specifically designed
to be turned with a 12 pt socket.
Fairly common in Aerospace, and ARP (Automotive Racing Products) got
their start by selling them as header bolts back in the '60s. I forget
which one, but there was a Chevy engine that was famous for having the
exhaust manifold bolts so close to the header tubes that you couldn't
get a socket on them. The 12 pt ARP bolts (with substantially smaller
heads) solved the problem.
Scott Hall wrote:
> alright, bolts. are the heads of these bolts spline, or 12-point?