In carpentry, what does 'keystone' refer to?

The term 'keystone' refers to the critical stone that is positioned at the apex of an arch, and it plays a vital role in maintaining the structure's integrity. Once placed, the keystone locks all other stones into position, allowing the arch to bear weight and remain stable. This is significant in carpentry, especially when constructing arches or curved frameworks, as the keystone ensures that the force is evenly distributed and helps prevent collapse. Understanding the function of the keystone is essential for carpenters working with architectural elements that require robust structural support.

In contrast, the first stone placed in an arch defines the initial position and alignment but does not provide the same structural benefits as the keystone. Decorative stones contribute aesthetic appeal without structural importance. Tools used for measuring dimensions serve a different purpose by ensuring precise cuts rather than contributing to structural integrity.