These specialized crayons are designed for use with Nettex harnesses and other systems that use click-in, click-out, or cotter pin mechanisms, providing a reliable way to monitor ram activity on farms. Formulated specifically for UK farming conditions, the crayons leave vibrant, visible marks that help accurately track mating. Each crayon typically lasts around two weeks, though this may vary depending on factors such as the ram's activity level and the temperature.