It looks like my old Weller Thermolock iron tip. Yes the sensor slips just inside the end of the tip.
A quick google shows the 'ET' series bits offered as suitable for the LR 21, FE 50, WEC, thermolock, EC2000 and EC2100 irons, so presumably any of those would fit.
https://uk.farnell.com/weller/et-b/t...-4mm/dp/416770