9/16 inch x 27 thread ef. Danco #74. 

The **PROPLUS GIDDS-2061513 Faucet Seat (25-Pack)** is a high-quality brass replacement part designed for Indiana Brass faucets, ideal for stopping leaks and restoring smooth faucet operation. These durable, corrosion-resistant seats ensure a reliable seal, making them perfect for plumbing repairs and professional maintenance. Compatible with various Indiana Brass models, this 25-pack offers excellent value for bulk repairs or long-term use.