The primary difference lies in the impurity threshold, specifically elements like lead (Pb), arsenic (As), and iron (Fe). Sn99.99 (High-Purity Tin) is essential for semiconductor manufacturing, high-end electronics soldering, and electroplating where even trace impurities can cause circuit failure. Sn99.95 (Standard Grade) is the industry workhorse, widely used for tinplate production, bronze/brass alloying, and general chemical applications. Buyers must specify the grade based on their end-product sensitivity to trace elements.