The part numbers you listed (ATP6.500-1LB, APN12-1, and APW1316N) are individual components rather than a pre-packaged vehicle kit. In the performance tuning world, this specific combination is most commonly used for:
Ford Falcon "Barra" 4.0L I6 Engines
This combination is a popular "custom" head stud solution for the Ford Barra (BA, BF, FG, FG-X) engine found in Australian Falcons.
The Component Breakdown:
- ATP6.500-1LB: A single 7/16" diameter stud with a 6.500-inch length.
- APN12-1: A 7/16-20 12-point chrome moly nut.
- APW1316N: A 7/16" parallel ground washer.
Why this specific setup?
Standard Barra head bolt kits (like the common ARP 203-4301) are usually 12mm. However, many high-horsepower builders "downsize" or "upsize" to 7/16-inch studs (like the ones you listed) because:
Strength: They are often made from ARP 2000 or higher-grade material to prevent head lifting under high boost.
Custom Length: The 6.500" length is specifically required when using certain aftermarket cylinder heads or thick head gaskets.
Other Potential Fits
Because these are "per-item" parts, they can also be found in
Holden V8 (304/308) engines: Some aftermarket alloy heads require this specific stud length.
Universal Racing Applications: Any engine block tapped for 7/16-14 threads that requires a 6.5" reach.
Summary: If you have a full set of these, you are likely looking at a heavy-duty head stud conversion for a high-boost Ford Barra or a modified Holden V8.