The discs are 2mm thick, thread - M2.5 - fits all systems with 2.5mm thread.
The threaded hole is slightly offset - this prevents the pendant (bead) from rotating on its own axis.
Size: 20 and 30mm
Matching mandrels can be found here: cabochon mandrel
You can find this shape with the thread in the middle here
You can find these discs seperately here
Material: stainless steel