train-bolt

In such case, however, the breeching should be frapped forward of the carriage, the ends crossed under the muzzle or otherwise arranged so as to keep the muzzle outside of the port; the side-tackles left loose; the chocking-quoins placed square up against the outer part of the front trucks; the train-tackle hauled taut, the end of the fall passed through the train-bolt and well secured, and wet swabs placed up against the forward part of the rear trucks and sprinkled with sand or ashes.

Ordnance Instructions for the United States Navy. 1866. Fourth edition. United States. Navy Dept. Bureau of Ordnance