Thermocouples are one of the most practical and widely used tools for gathering time/temperature data in thermal processing environments. Ranging from laboratory-scale experiments to full industrial heat-treatment operations, these sensors provide direct insight into how materials respond to heating and cooling cycles. By embedding or attaching thermocouples to components, engineers can capture transient thermal histories that reflect the furnace conditions and the complex system of conduction, convection, and the thermal effects from phase transformations within the material. One important application of this data is for calibration of boundary conditions such as convective heat transfer coefficients (HTCs) used in computational models to simulate the heat transfer in the process that are otherwise difficult to measure directly. Despite their utility, thermocouples are not passive measurement tools. Their physical presence, particularly the geometry and placement of the thermocouple wire, can influence the temperatures they record. One notable phenomenon is the “fin heating/cooling” effect, in which the thermocouple wire acts as an extended surface that enhances the local heat transfer. This can distort recorded temperatures and introduce systematic error into both experimental interpretation and subsequent modeling efforts. The present work examines this effect in detail through a combination of finite element modeling and fitting to ultimately quantifying the fin effect and to propose practical mitigation techniques.