When evaluating H4 sockets, the primary focus should be on heat resistance and electrical conductivity. Ensure the ceramic base is made of high-frequency porcelain or steatite, which can withstand temperatures exceeding 200°C to 300°C without melting, unlike plastic alternatives. The internal terminals should be made of pure copper or phosphor bronze with tin or silver plating to ensure low resistance and prevent oxidation. Additionally, verify that the wiring uses high-temperature resistant silicone or Teflon-coated cables (typically 14-18 AWG) to handle the current load of high-wattage halogen or LED bulbs.