Wilwood Copper Soft Tempered Washer - 0.406in ID x 0.625in ID

This is a Wilwood Copper Soft Tempered Washer, part number 240-5227. It's designed to help create a seal when you're connecting components with straight thread or banjo style fittings, like brake lines or fittings on a master cylinder. The copper construction is soft and tempered, which allows it to crush and conform to the surfaces it's pressed against, ensuring a leak-free connection.

When you're working on brake lines or other fluid transfer systems, a good seal is critical to prevent leaks and maintain proper function. This washer is made from copper, a material known for its malleability, which helps it form a tight seal under pressure. The tempered nature of the copper means it's strong enough to hold that seal without deforming permanently under normal operating conditions.