The Top Marks Ram Crayon System has been designed for both comfort and ease of use. Crayons 'click in' and out of the harness with no fiddle cotter pins. Cold crayons are softer for use in temperatures below 16ºC. Crayons leave a bright, clear mark to assist with flock management and track ram activity. Each crayon will generally last at least two weeks but is affected by temperature and ram activity. The shelf life of this product is 4 years.