Most 3/8" header bolts came out years ago with 7/16" wrench flats on them. Pretty standard for many years. If you ever messed with headers, you knew this.
A dozen years ago, the went to 3/8" wrench flats on the bolts to fit a wrench in between tube bends easier. It helped in most cases.
In just the last 2 years or so, they have further reduced the wrench flats area to a 5/16" wrench. It's amazing how much of a difference it makes. What we used to struggle with on race cars we now use a ratchet and socket.
I also use the small wrench header bolts wherever you need some room for access. SBF fuel pump bolts and coil mounts are 2 areas they help.
I get them from Shoenfeld headers when we buy new headers. Most bolt makers are selling them now.
Left to right is 5/16 head, 3/8 head and 7/16 head bolts.
Enjoy your day.
SPark
