A sex bolt, (also known as a barrel nut, barrel bolt, Chicago screw or post and screw), is a type of fastener (nut) which has a barrel-shaped flange and protruding boss that is internally threaded. The boss sits within the components being fastened, the flange provides the bearing surface. The sex bolt and accompanying machine screw sit flush on either side of the surfaces being fastened. It is normally chosen because of its low profile compared to other nuts. The sex bolt often has a built-in feature, such as a slot, to aid in tightening the fastener. Some sex bolts, more commonly known as architectural bolts, have knurled barrels to allow one-sided assembly. Binding posts are similar to architectural bolts in that they are designed to be assembled from one side, but they have teeth on the flanged surface to keep them fixed.
They were originally designed for the printing industry to bind large catalogs and plastic sleeves together.
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