On Tue, 01 Mar 2016 09:28:46 -0700, Don Y
wrote:

On 3/1/2016 9:07 AM, dpb wrote:
On 03/01/2016 9:44 AM, Don Y wrote:
....

It doesn't matter whether I'm looking to replace just the slab
(reusing existing frame) *or* replacing the entire frame (with
a prehung unit) -- if the RO is sized too narrow!

The remedy available to me is to replace/revise the buck; or,
fabricate a thinner jamb (assuming that to be a cheaper solution
than a custom 35.5" metal door).

I'm not keen on letting this turn into another long-winded
back-and-forth where we play 20 questions and roam around
visiting all sorts of different issues that MAY or MAY NOT
be pertinent.

"A stock 36 inches door is 36 inches -- whether a slab or
(effectively) when prepackaged in a prehung jamb"

That's all I need to know to sort out what I have to do...

Excepting it already has in large part owing to your reluctance to outline the
actual objective and specifics of the condition.

We've already established that nominal 36" doors aren't necessarily either 36"
_or_ 35.5" and that you can undoubtedly find either. That still leaves open
all the other dimensions and details that are just as important as far as what
would have to be done to make a swap.

I'd think the likelihood the RO is too narrow pretty low but it is possible,
yes. Have you done enough exploratory work to know what the RO dimensions
actually are? You may be making mountains from molehills and the simplest
solution is to simply rip out the old and put in a new prehung stock unit.

I can trace the grout lines to know how large the opening in the
*masonry* is. I can see where the door "begins". I can do simple math
to determine how wide the buck+frame are.

I can then examine the "assembled dimensions" of prehung doors to see
how they would fit.

Ripping out the old leaves me with a large, person sized hole in
the house that needs to be filled before the next nightfall. I'm
sure as hell not keen on doing that just to "gather data".

I'm an engineer; I can look at numbers on a piece of paper and
sort out how things will (or won't!) work without having to
"try it and see!"

The easiest way to determine a masonry R/O is to drill a small hole in
the jamb near the stop and probe with a wire. You can easily fill that
hole and make it disappear if you decide not to replace the jambs.
You might find there is quite a bit of bucking in that opening.