What is the minimum diameter for a Tell-Tale hole in a stay bolt?

The minimum diameter for a Tell-Tale hole in a stay bolt is 3/16 of an inch. The purpose of the Tell-Tale hole is to provide a visual or audible indication of water or steam leakage from the boiler or pressure vessel, which helps in monitoring the integrity of the stay bolts. A hole that is too small may not allow sufficient fluid to escape, making it difficult to detect leaks, while a hole that is too large could compromise the structural integrity of the stay bolt.

In the context of design and safety standards, 3/16 of an inch is a balance between effective leak detection and maintaining the mechanical strength required for stay bolts, which are essential in supporting the structure of a boiler or similar equipment. By adhering to this minimum size, engineers ensure that the design remains reliable, safe, and within accepted engineering practices.