It's on the top of the immersion lance,used for connecting the thermocouple to the lance.

connector:

All the positive polenegative pole and the down-lead of the connectors plug core are used compensation type,that means all of them are made from relative compensating cable materials. They are separated into type SC(RC),type BC and type WRe3/25(D)WRe5/26(C).

They are separately matched with Pt10Rh-Pt(Pt13Rh-Pt)Pt30Rh-Pt6Rh and WRe3-WRe25WRe5-WRe26 expendable thermocouple.

Type 602 connector  can just match type 602 thermocouple.

Specification:1.Type:KS/KB/KR/KW3-25/KW5-26