Machined from rustproof aluminum material, then anodized for lasting protection. For laying out your smallest circles to the large ones (up to 100” in diameter). Arms are precisely aligned with spring tension joints to guarantee accuracy and rigidity for years of continued service. The holder accommodates flat or round soap stone and pencils. Small and medium models fold to pocket size. The Extra Large model can be adjusted tight in the center to eliminate any movement while marking large radius’s or circles.