Product: This is a sinuous spring (commonly called a zig-zag spring), which is the primary support system in the seat and back of most sofas. It's a continuous, pre-bent steel wire that is fastened to the wooden sofa frame.

"Flat Straight": This refers to the ends of the spring being left straight and unbent, making it easier to attach to the frame with clips or staples before the main "zig-zag" pattern begins.

3.6mm Thickness (≈9 Gauge): This is the most critical specification. This is an extremely heavy-duty, commercial-grade wire diameter.

• Standard Residential Use: 1.8mm - 2.5mm (13-18 gauge)
• Heavy-Duty Residential/Commercial: 2.7mm - 3.2mm (10-12 gauge)
• 3.6mm (≈9 Gauge): This is for extra-heavy-duty commercial applications where maximum weight capacity and unparalleled durability are required (e.g., waiting rooms, airports, theaters, large-capacity public seating).