What is used to attach a grease gun to the Zerk fitting of a bearing housing?

The correct answer is the coupler, which is specifically designed to connect the grease gun to the Zerk fitting, allowing for an effective and secure means of lubrication. The coupler's design enables it to easily grip the Zerk fitting, providing a leak-free connection while facilitating the transfer of grease into the bearing housing. This ensures that the lubricant can be applied correctly and efficiently, which is essential for maintaining proper bearing function and prolonging its lifespan.

Using a coupler is advantageous as it is often designed to be quick-release, making it easier for operators to connect and disconnect the grease gun while minimizing the mess associated with grease application. The other options, while related to connecting or fastening components in technical contexts, do not specifically fulfill the required function of linking a grease gun with a Zerk fitting, making the coupler the most appropriate choice for this application.