Machinist

[Lawrence London <lfljvenaura@gmail.com>]

What to look for in Geometric die head?
http://www.practicalmachinist.com/vb/general/what-look-geometric-die-head-283802/
http://www.practicalmachinist.com/vb/general/what-look-geometric-die-head-283802/index2.html

71 page .pdf copy of “Geometric Standard Screw Threading Manual” Covers all their Die & Tap heads
http://www.qualitychaser.com/qc_dload.html
http://www.akon-werkzeuge.de/doc/brochure%20Rubometric.pdf

"Screw Thread Production to Close Limits by Howard Adt"

Nice find! Lots of good info there. Free to download.
Screw Thread Production to Close Limits: Manufacturing Methods of Threading ... - Howard Elsworth Adt - Google Books
https://books.google.com/books?id=WL9CAAAAIAAJ&pg=PA3&lpg=PA3&dq=Screw+Thread+Production+to+Close+Limits+by+Howard+Adt&source=bl&ots=CD8K0OU8_q&sig=2MgQTqJtoK1zyBBHMcZ7YPm3kh0&hl=en&sa=X&ei=zutXU67BBJW1yATpj4CwAw#v=onepage&q=Screw%20Thread%20Production%20to%20Close%20Limits%20by%20Howard%20Adt&f=false

stick with the D type heads D, DS,DSA all use the same chasers in there head size

You can also get chasers (standard and projection) from these guys. Sometimes NOS and regrinds. Good to deal with. Complete heads too.
Detroit Automatic Tooling, Inc
http://detroitautomatic.com/

Here's one of many old posts on the subject.

Geometric Die Head - DS or DSA?
http://www.practicalmachinist.com/vb/general/geometric-die-head-ds-dsa-187997/

I think today unless you get all the chasers you will ever need with a different brand, that a Geometric DSA is the most practical unit to own.
http://www.practicalmachinist.com/vb/general/geometric-die-head-ds-dsa-187997/

The aligning shank is available on both the DS and the DSA, as shown in these drawings from the Geometric manual. The DS is on the left, DSA is to its right.
The DSA has a calibrated depth adjustment scale on the side which the DS lacks. A photo of the scale on my DSA is on the right.
http://www.mayadate.org/pix/Geometric_DSA_Drawing.jpg
http://www.mayadate.org/pix/Geometric_DSA_Mine_Crop_3x3@72.jpg
http://www.mayadate.org/pix/Geometric_DS_Drawing.jpg

I can't answer your question, however here is a link to download a copy of a Geometric Threading manual. It is 8 meg, 71 pages with information on the different Geometric heads, setup, usage, and parts breakdowns.