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

Thermocouple 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-602; KW3-25/KW5-26-602