The US FDA’s proposed rule on laboratory-developed tests: Impacts on clinical laboratory testing

A compass saw

A compass saw is a type of saw used for making curved cuts known as compasses, particularly in confined spaces where a larger saw would not fit.^[1][2]

Compass saws have a narrow, tapered blade usually ending in a sharp point, typically with a tooth pitch of 2.5 to 3 mm (eight to ten teeth per inch),^[2] but down to 1.3 mm (up to 20 teeth per inch) for harder materials and as long as 5 mm (as few as five teeth per inch) for softer materials.^[1] They have a curved, light "pistol grip" handle, designed for work in confined spaces and overhead.^[2]

The blade of a compass saw may be fixed or retractable, and blades are typically interchangeable. Partially retracting the blade can prevent flexing and breaking when cutting harder materials.^[1]

Compass saws are suitable for cutting softer woods, plastic, drywall, and non-ferrous metals.^[1][2] The pointed tip of the blade can be used to penetrate softer materials without the need for a pilot hole.^[1]

Compared with other saws designed for cutting curves, such as coping or fretsaws, compass saws have a larger blade and longer pitch (fewer teeth per inch). This allows them to cut faster, and to cut through thicker materials, but leaves a rougher finish.^[2]

Compared with drywall saws, compass saws typically have a longer blade – at 15 to 30 centimetres (5.9 to 12 in) – and shorter pitch (more teeth per inch).^[1][2]

Keyhole saws, also called padsaws or jab saws, feature shorter, finer blades and (often) straight handles, and are suitable for cutting extremely tight curves.^[2][3]