Siemens SIMATIC NET PROFIBUS Owner's Manual page 115

Note
If you connect to screw terminals, the stranded cores must be fitted with wire-end
ferrules (0.25 mm
materials with permanently stable contact properties, for example copper with a
tin-plated surface (not aluminum).
The bus connector 6ES7 972-0BA30-0XA0 cannot be connected to the stranded
cores.
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Passive Components for RS-485 Networks
2
complying with DIN 46228). Use only wire-end ferrules made of
4-17