Petard, a brass pot fixed upon a strong square plank, which has an iron hook to fix it against a gate or palisades

Print shows a bomb-like device used to blow apart doors or gates.

Caption continues: This pot is filled with powder; which, when fixed, breaks every thing about it; and thereby makes an opening to enter the place.
Illus. in: A new military, historical, and explanatory dictionary ... / Thomas Simes. Philadelphia : Sold by Humphreys, Bell, and Aitken, 1776.
Published in: The American Revolution in drawings and prints; a checklist of 1765-1790 graphics in the Library of Congress / Compiled by Donald H. Cresswell, with a foreword by Sinclair H. Hitchings. Washington : [For sale by the Supt. of Docs., U.S. Govt. Print. Off.], 1975, no. 912.