Robin Renzetti - Stefan Gotteswinter -style
interweb:
http://gtwr.de/projects/pro_rore/index.htmltube:

materials on first parts:
* Indicator clamp S.G. "1.2767 toolsteel and will later be hardened to about 45..50HRC:"
I used 15 mm OD silver steel, Böhler K510 SILVER STEEL - 1.2210
Main driver being that I don't have Keats/prism chuck and it needs a turned feature to start with. 15 mm round has over 10 mm square hiding inside and screaming to be released.
*10 mm ball
S.G. used hardened balls and grilled them with HM-drill. I don't have drill that eats hardened steel for lunch, ordered 10 mm relaively soft balls:
https://simplybearings.co.uk/shop/p221140/10mm-Diameter-Grade-100-AISI-316-Stainless-Steel-Ball-Bearings/product_info.html10mm Diameter Grade 100 AISI 316 Stainless Steel Ball Bearings
AISI 316 Stainless Steel with a hardness of 25 - 39 Rockwell Scale equivalent to 140 - 160 HB (Brinnel Scale).
..
Unhardened austenitic stainless steel with good corrosion resistance to sea water, dilute nitric, sulphuric and acetic acids, photo chemicals, inks, bleaches, dyes etc.
Can be machined / drilled