What tool is best suited for securing a string line at different heights?

The line pin is the most appropriate tool for securing a string line at various heights. It is specifically designed to anchor the string line in place, allowing for precise alignment when laying out masonry work. The line pin can be easily driven into the ground or a masonry surface, providing a sturdy point to attach the string line. This capability is essential for ensuring that the line remains taut and at the correct height throughout the construction process, thus aiding in achieving level and straight masonry work.

Using other tools listed would not serve the specific purpose of holding a string line. A trig, for example, is typically a tool used for measuring angles rather than securing lines. A trowel is primarily used for spreading mortar or plaster, and a bolt cutter is designed for cutting through metal or wire, making them unsuitable for this particular task. The effectiveness of the line pin in maintaining the string line at adjustable heights directly contributes to the accuracy and quality of the masonry layout process.