A bolt is a form of threaded fastener with an external male thread. Bolts are thus closely related to screws but should not be confused with screws. Bolts that have a loop (also called eye) for a head are called ‘eye-bolts’ The ‘eye’ is required to provide a point of purchase for the attachment of fastening equipment such as a rope or a cable.We have M6 to M72 in three varieties DIN 580, EN8 & MS.