T 6 – trapez, closed quicklink of stainless steel by Peguet company:

• work load up to 450 kg,
• breaking load: 2250 kg
• fits risers of 20-25 / 30-35 mm width

Trapez is used for example to attach V-riser to the harness. Of course you can use squares for that too – all depends on actual set (especially width of the risers and harness straps).