A Robertson screw, also known as a square head screw or a socket head screw, is a type of screw used to fasten materials together. The square head of the Robertson screw provides a better grip for the screwdriver and reduces the likelihood of the screw slipping or stripping. This type of screw was invented by Canadian P.L. Robertson in 1908 and has gained popularity in North America, particularly in the construction industry. While the term "Robertson screw" is the most commonly used name, other synonyms may include "square drive screw," "quadrex screw," or "scrulox screw," depending on the particular brand or manufacturer.