Precision ground, quenched, and tempered.
All popular heavy-duty chucks manufactured by Schunk, Forkardt, Röhm, and SMW (with sharp serrations).
Forkardt: NH 250-315, NHF 250-315
Schunk: TH/THF 250-315, HSL 250-315
SMW: HFKS 250-315, HFK 250-315
Socket head screws DIN 912 - 12.9!
Other T-nuts available ex works.