HSN classification sets goods coding; turnover thresholds determine required code detail; services classified under SAC. Goods are classified under GST using the HSN code: taxpayers above a lower turnover threshold but below a higher threshold must use a two digit HSN code, taxpayers at or above the higher threshold must use a four digit HSN code, and taxpayers below the lower threshold need not mention HSN on invoices. Services are classified under the Services Accounting Code (SAC).