combinations of different thread types

[geneticmaterial]

Sorry of this is in the wrong section.
Hi, I am looking to adapt a car intake manifold.
There are 4 injector holes (untapped) that measure a touch over 18.5mm.
I plan to tap these holes and fit some reducing nipples to them.
I have a 7/8" BSW tap bit and some M20x2.5 ISO tap bits.

I need some help on the following;
Will the 7/8" bsw be too large for this hole?
if not, what other threads would work with the 7/8 bsw?

If I use the M20x2.5 bit instead, what other male threads would work with it?

The reason I'm asking this is because these are the only bits I have but I am struggling to find nipples or reducers that fit with either the 7/8" bsw or the M20x2.5 bit.

Thanks

Dan

 

[MikeHalloran]

A Google search on | "7/8" BSW dimensions | found some useful information.
The 7/8" BSW thread requires a tap drill of 19.25mm diameter, so you can cut a full thread of that size.

Similarly, a Google search on M20 x 2.5 dimensions told me that
the tap drill for M20x2.5 is 18.5mm, so you can't cut a proper thread starting with a hole much larger than that. Much, in this case, would be the normal amount by which a drill cuts oversize, or about .002 inches or .05mm.

Just out of curiosity, what are you trying to adapt the manifold to do?


Mike Halloran
Pembroke Pines, FL, USA