When sourcing RTDs, the most critical factor is the element type, with Pt100 and Pt1000 being the industry standards due to their stability. You must specify the Accuracy Class (Class AA, A, or B according to IEC 60751); for high-precision laboratory or pharmaceutical needs, Class A or better is mandatory. Additionally, consider the wiring configuration (2-wire, 3-wire, or 4-wire)—3-wire and 4-wire systems are preferred in B2B applications to compensate for lead wire resistance and ensure measurement integrity.