trunnion-square

A trunnion-square of steel or iron for ascertaining the position of the trunnions, with reference to the axis of the bore.

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

The trunnion-square is then placed upon the trunnions in the plane of their axis.

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

The axis of the trunnions is to be laid horizontal, either by placing a small level on the trunnions, or, as more exact, by using the trunnion-square.

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

If the trunnion-square is used it will be proper to verify the position of the line of sight, which is frequently incorrectly placed at the foundries.

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

If the alignment of the trunnions be correct, it will serve as a means of determining the correctness of the line of sight, which, before the gun is removed from the lathe, should be distinctly traced on the sight-masses and the swell of the muzzle, and should be at right angles to the base-line, to the axes of the trunnions, and to the connecting piece of the trunnion-square, when its branches rest against their rear, with the plates across their upper surfaces.

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