<p style=”text-align: left;”>I have a set of them and I’ll grab a snap in a bit to show the holders.</p>
Very good for the small boring jobs I get occasionally.

We have hundreds of them at the museum, about 20 Iscar that I bought years ago and the rest were Sandvik, brought in by Gary, boring, grooving and threading. All the same style shanks as Jasons. I have added Densimet tungsten shanks to some to use in the mill boring head as well as in the lathes. We can bore down to about 4mm diameter.

Here is a thread from a German forum with dimensions and various ways to hold the Horn 105 system bits. I have a couple hundred of them I bought used but re-sharpened, they are very handy

Most browsers have an autotranslate option that works quite well.

https://forum.zerspanungsbude.net/viewtopic.php?f=59&t=44478

and a .pdf of holders at:

http://herbert-schmitz.net/Zerspanungsbude/Horn.pdf

Wade

The scaling of the photo is probably a bit off which gives those numbers, the second link gives 4.8mm and 2.5mm for the hole so may also be some clearance as it is the two flats that make contact. Had they been US made I might have said 3/32 and 3/16

You can get these tools with round shanks which would then just need a simple sleeve. Possibly drill the sleeve side so the grub screw bears on the tool.