nut

In marine anchoring, the nut is a rigid projection cast or forged onto each side of an anchor shank, positioned just above where the stock (the crossbar) passes through. Its sole function is mechanical: it acts as a stop to prevent the stock from sliding along the shank. Without these nuts, the stock could shift under load, destabilizing the anchor's holding geometry and rendering it ineffective on the seabed.

The nut bears against a collar or groove that exists on the stock shaft itself. When the anchor is set and the flukes dig in, tension in the cable pulls the shank, but the stock is held in its perpendicular position by this contact. The two nuts, one on each side, ensure symmetrical restraint and prevent any rotational or longitudinal drift of the stock relative to the shank.

Nuts are typically low-profile, rounded bosses rather than sharp protrusions, since any acute edges would concentrate stress and risk fracture under the heavy cyclic loading anchors endure. In wrought-iron or cast-steel anchors, they are integral to the shank itself. The size of the nut, its thickness and diameter, must match the cross-section of the stock and the expected holding loads. Undersized nuts create a weak point; oversized nuts add unnecessary weight and cost without benefit.

The nut is sometimes confused with the ring or eye at the crown of the anchor where the cable connects, but these are entirely different features serving entirely different purposes. The nut is at the shank-stock interface; the ring is at the top of the shank.

This terminology comes from engineering analogy to threaded fastener nuts, though a ship anchor nut involves no threads. The term has been standard in anchoring manuals and marine salvage work for over a century, and it appears in classification society rules and shipbuilding specifications wherever stock-and-shank anchors are used.