Hot Rods C-357-B EDELBROCK triple deuce manifold question.

Does anyone out there know what the thread / bolt size is for the threaded bosses on the above manifold which is a modern version that is still being sold new, - ( not one from the 1950’s )

Particularly the right hand side ( rear ) boss that is under the vacuum can on the distributor.

It appears that they are all tapped differently and I can’t find a bolt to suit.
1/4 unf slides down inside and 5/16 unc won’t thread in as it seems too large.

Metric bolts 8mm appears too large and 6mm too small.

Is it possibly an oddball thread type, such as whitworth or something else ?

any help would be appreciated, - thanks !

 

Is it possible it’s pipe threads ? 1/4 npt

 

In guessing here, but maybe it is supposed to have a thread insert? Depending on what bolts on there, I would just run a 5/16 tap in it and call it good.

 

I would think 1/4" NPT. I see you are from New Zealand, it's not identical but very similar to 1/4" BSP

 

If it’s new I’d double check it’s not 5/16 UNC.

 

The NPT description means National Pipe Taper, 1/4”NPT is 1/4” ID pipe and the tapered thread, when measured at its midpoint will be approximately .530, so its not that.
If you chamfered the hole a bit would the 5/16 bolt start in the thread?

 

PDF install sheet makes no mention of it. Not what you like but is it for a temp sensor for engine management? If so, what thread do those sensors use?

 

^^^^^ A little more poking around???

 

It's just a 5/16" threaded boss that doesn't go into water. Try running a tap in the hole to straighten out the boogered up thread's.

 

^^^^^ Then is it for ground wires?

Not that I wanna know, because if I did I’d call Edelbrock myself.

 

yes, correct, that is the manifold, I downloaded a photo and then got distracted and forgot to post it.

not open to any p***ages, just a boss and I wanted to put a clamp into it to hold a vacuum line.
On the left hand side, the two bosses ( ***uming to hold throttle linkage) are both different sizes and the rear one appears to be the same as the one that I am questioning.

sorry for the late responses, but we are on a bit of a time difference here.
It was 11.00 pm here when I posted (and then I went to bed).

 

Thanks, - we have NPT here, ( and not a tapered thread) and I didn’t try that, but I think that the thread is too co**** for npt.

Can’t get a 5/16 UNC or UNF started.

 

maybe, and that is what I thought it was, just measures smaller.
At the moment the distributor is in the way, so that is the plan, to re tap a 5/16 thread
if no one can convince me that it is something out of the norm, which of course is why I asked first.

 

thanks,
I did download the PDF sheet before I posted this thread, and like you, I couldn’t find any information about it.

 

It is chamfered, and I still can’t start it.
I will just re tap it.

 

8mm?

 

Thank you gentlemen for all of your replies.

as mentioned, I will probably just re tap, or if it is actually 5/16 UNC thread, just clean it up……..

 

tried that also !
( I tried a lot before I asked here).
It measured and looks like 7mm x 1.25, but I don’t think there is such a thing.
I ***ume that they are made in America so will be standard imperial 5/16”.
If made overseas it is more likely that someone could have inadvertently taped it with metric instead of imperial.
Or -
Maybe their tap is worn out, hence a smaller hole………..?

 

None of it makes sense. Why is it there to begin with? And do we really want to know?

 

Pretty sure this is the manifold I have sitting on a shelf, I’ll check when I get home after work.

 

There is an M 7.0 co**** thread

 

Mine seems to be the mirror image in the back of the one pictured above and the hole is not tapped. Is mine the older version??

 

Yours makes sense when used on a 55 Chevy car. Trucks may have used that sensors position longer.

Here’s both 2 and 4 barrel intake’s

 

Hmmm, it is a bucket list car, better hang on to it. Lol

 

Can you get a thread pitch gauge in it?

 

1/8" npt is 27 threads per inch and female ID .380". It is often used for gauge line

 

As has been said, it's a 5/16" course thread hole. As for your desire to use it to hold a vacuum line, that's how I used it as well. I made a small L-bracket out of stainless steel.

 

thanks for confirming this.
At the moment I have run it around the other side and will just use a non traditional rubber clamp.
I still don’t understand why on the other side the two holes are different ?
Curious to know what yours are ?
Although it is possible that they are both meant to be 5/16” co**** and the thread has been crossed and someone tapped it out to 3/8” co****.