6 Best Line Blocks for Keeping Courses Straight

Maintaining perfectly straight lines across a sprawling roof deck or a long fence run is the hallmark of a professional-grade installation. When a layout drifts even a fraction of an inch, the resulting aesthetic errors become impossible to hide as the job progresses. Using high-quality line blocks ensures that the mason’s line stays pulled taut and perfectly level, preventing sagging that ruins layout accuracy. These simple tools provide the necessary tension control and alignment that every tradesperson needs to deliver high-quality work.

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Bon Tool 12-251 Wood Blocks: The Pro’s Go-To Choice

Hardwood line blocks remain a staple on job sites because of their reliable grip and natural durability. The Bon Tool 12-251 units offer a classic, dense wood construction that bites into the masonry or framing members, holding tension without slipping under the pressure of a long line.

Wood blocks are particularly effective because they do not deform under the high tension required for long, horizontal runs. Unlike cheaper composites, these blocks maintain their structural integrity even when exposed to high heat or direct sunlight, which can soften lesser materials.

The bottom line: if the preference leans toward a traditional, no-nonsense tool that provides a solid, immovable anchor point, these wood blocks are the gold standard. They perform best when paired with high-tensile braided nylon lines on standard brick or block wall layouts.

Kraft Tool Co. PL325: Best Value Plastic Line Block

For the contractor who needs a reliable, lightweight solution that won’t break the bank, the Kraft Tool Co. PL325 is a frequent choice. These high-impact plastic blocks provide a consistent surface area that is easy to handle while wearing thick work gloves.

The primary advantage here is visibility; the bright material stands out against dark underlayment or rough lumber, reducing the chance of losing a tool in the debris. Because they are molded from high-density plastic, they are immune to moisture absorption, preventing the warping or rot that can affect wood blocks over time.

While they are excellent for residential siding and standard brickwork, they may occasionally shift if the line is pulled to extreme tension. These blocks are best suited for everyday layout tasks where speed and accessibility are the priorities.

Marshalltown Corner Blocks: For Perfect Outside Corners

Maintaining a consistent corner profile is perhaps the most difficult aspect of masonry and siding alignment. Marshalltown blocks are specifically engineered to sit flush against outside edges, providing a clean pivot point for the line to wrap around.

These blocks prevent the line from digging into the edge of a brick or a soft siding material, which protects the aesthetic finish of the project. By using the dedicated groove, the line remains perfectly perpendicular to the vertical face, ensuring the corner remains square from the base to the cap.

Avoid the temptation to use a standard block on a corner, as it will often sit unevenly and create a slight bow in the line. For any project where a corner will be exposed and visible, a specialized corner block is a mandatory addition to the tool belt.

A. Richard Adjustable Line Stretchers: Most Versatile

When working on irregular surfaces or projects that don’t offer standard anchor points, adjustable line stretchers provide the flexibility required to get the job done. The A. Richard system allows for precise tensioning adjustments without needing to unwrap and re-tie the mason’s line constantly.

These are particularly useful when installing siding panels where the anchor points need to be moved frequently to accommodate varying panel heights. The ability to lock the line in place with a thumb screw makes them a favorite for tasks that require frequent stops and starts.

Understand that these units have more moving parts than static blocks, meaning they require occasional cleaning to keep the tensioning mechanism free of grit. They represent the best choice for complex layouts that demand constant, incremental adjustments.

C.H. Hanson PRO-SHIELD: Best for Heavy-Duty Use

The C.H. Hanson PRO-SHIELD blocks are built for high-tension applications where standard plastic or wood might succumb to the pressure. They feature reinforced construction and ergonomic contours that allow a user to pull the line tight enough to eliminate even the slightest center-point sag.

These blocks excel in commercial settings where long spans of masonry or metal paneling are common. The design prevents the line from binding, ensuring the tension is distributed equally across the entire run rather than bunching at the block itself.

If the project involves long, heavy-gauge steel or thick brick walls that require significant tension to keep the run true, skip the economy options and invest in this level of durability. They are built to withstand the rigors of heavy daily use without cracking or losing their grip.

StringA-Level Pro Pack: Best System for Siding Layout

The StringA-Level system is a specialized solution that goes beyond basic line blocks to act as a comprehensive alignment tool. It is specifically designed to prevent the sagging issues common with long horizontal siding runs by incorporating a vertical support mechanism.

This system is an ideal choice for installers who frequently switch between different board widths or exposure settings. By using the integrated level attachments, the installer can ensure the line is not only taut but also perfectly level across the entire face of the building.

While this system requires a slightly higher upfront investment, it drastically reduces the time spent on manual layout checks. It is the most robust option for exterior trim and siding jobs where a deviation of even an eighth-inch becomes glaringly obvious.

Wood vs. Plastic Blocks: Which One Is Right for You?

Choosing between wood and plastic is largely a matter of the environment and the intensity of the work. Wood provides a superior “tooth” that grips masonry surfaces firmly, making it excellent for bricklaying where the block rests against the material itself.

Plastic blocks, however, are essentially maintenance-free and often feature better ergonomics for rapid, repetitive layout work. They are the clear winner for exterior siding or framing where moisture and exposure to the elements would shorten the lifespan of a wood tool.

Consider the climate as well; in high-humidity zones, wood blocks can swell and become difficult to work with. If the job site is subject to frequent rain or damp conditions, stick to high-impact plastics to ensure consistent performance throughout the project.

How to Properly Set and Tension Your Mason’s Line

Setting a line correctly involves more than just pulling it tight; it requires an understanding of how to manage the “pivot” points of the structure. Always secure the line at a fixed point, then move to the block and apply tension until the line “sings” when plucked lightly.

Avoid the mistake of pulling the line so tight that it bows the material or puts excessive strain on the corners. The goal is to reach a state of high tension where the line remains perfectly straight, but not so high that it creates an uplift risk or snaps prematurely.

Periodically check the tension throughout the day, as temperature swings can cause materials to expand or contract. A line that is perfectly tight at 7:00 AM may develop a slight sag by midday, so keep the block accessible for quick adjustments.

Choosing Your String Line: Braided vs. Twisted Nylon

The line itself is just as critical as the block holding it. Braided nylon is generally superior for most applications because it resists fraying and holds tension more consistently than twisted alternatives.

Twisted line can stretch unevenly under heavy loads, which often leads to inaccurate layout marks as the tension changes. Braided line maintains its shape and diameter, ensuring that the measurement from the line to the surface remains precise across the entire run.

For the best results, use high-visibility neon colors—yellow or orange—so the line remains easily visible even in low light conditions. Keep a spool of high-test braided nylon in the tool box, and replace it as soon as any signs of fraying appear to prevent a line snap during critical installation stages.

Beyond Shingles: Using Line Blocks for Shingles & Fences

Line blocks are surprisingly versatile tools that find utility well beyond their primary use in brickwork. When installing fence rails, they are indispensable for ensuring each section follows a perfect horizontal plane, especially on long, uneven fence lines.

On roofing projects, specifically when laying out horizontal courses for metal panels or wood shakes, they keep the layout consistent from the drip edge to the ridge. Without them, it is nearly impossible to prevent the layout from “creeping” or wandering as the work progresses up the roof slope.

Regardless of the project, the fundamental principle remains: the line is only as good as the anchor. Investing in quality line blocks ensures that the foundation of the work—the alignment—remains rock-solid, leading to a professional finish that stands the test of time.

Selecting the right line block is an investment in the precision of the entire project. By matching the tool to the specific demands of the materials and the environment, you ensure that the layout stays true from start to finish. A well-tensioned line is the most effective safeguard against common aesthetic errors, proving that even the simplest tools often provide the most significant impact on the final quality of the build.