Fastenings

parts for fixed connection of machine parts and structures. Parts of threaded connections, such as bolts, screws, studs, pins, nuts, wood screws, lag screws, washers, and cotter pins, as well as dowels, are included in the category.

The main parameter of threaded connections is the thread, whose shape and dimensions conform with standards. Bolts, nuts, and washers are used in bolted connections that do not require the cutting of a thread in the parts being joined. How-ever, space for the bolt head must be provided. Screws and studs are used in cases where location of the bolt is difficult or a hole through the part is undesirable. Washers are placed under nuts or bolt heads to prevent deformation of the parts being joined, to avoid scratching during tightening of nuts and screws, and to close the gap between the shank of the bolt and the opening provided in the part. Lock washers and cotter pins prevent loosening of bolts and nuts caused by vibration and impact. Fastenings are widely used in all branches of machine building. The size and shape of fastenings are standardized within each country, which is taken into account in manufacturing equipment for export.

In the USSR the current standards cover the types and sizes of mass-produced fastenings. Parts whose shape and size are determined by specific design consideration and by operating conditions, such as connecting rod bolts, are excluded from all-Union standardization. However, even for special fastenings the thread is usually standard. Standardization of fastenings facilitates their manufacture by multiple machining in factories producing metal articles.