Open end thermocouples should be sealed with a moisture sealant such as “Thermoseal” after conductors have been exposed prior to attaching leadwire. A small, easily assembled transition fitting for adapting sheathed, mineral oxide insulated thermocouples to leadwires. the leadwire adapter completely encapsulates the transition splice forming an insulating shield and providing an effective strain relief. The adapter provides for secure mounting on the sheathed thermocouple and a spring allows the leadwire to flex in a large radius bend thus eliminating wire breakage. Due to the fact the transition is enclosed within the adapter it is both moisture proof and vibration and shock resistant. Assembly is quite simple and may be performed in the field as easily as in the shop. No special tools are required, aside form the basic materials – soldering gun or torch, flux, soft or silver solder and a small amount of epoxy resin or potting material. A small staking tool may be used if desired to stake the ferrule and sleeve together. Open end of sheathed thermocouples should be sealed with a moisture sealant such as “Thermoseal’, after conductors have been bared prior to attaching leadwire.