Not all hinges are created equal. For casement windows, awning windows, and certain types of projected windows, the hinge mechanism determines not only how smoothly the window operates but also how well it seals, how securely it locks, and how long it will last. Two common hinge types dominate this category: the two-bar hinge​ and the four-bar hinge. While they may look similar at a glance, their differences in design, performance, and application are substantial.