An M-1000 Quarter Stick is a large firecracker that falls within a certain range of dimensions that carry 30 grams of flash powder. These dimensions typically are 3/4" x 3.5" or 1" x 2.5". Like all the others preceding it, you will see Visco fuse from varying lengths protruding from the side or end depending on the manufacturer.
The term quarter stick is based on a quarter-stick of dynamite, which it somewhat resembles. However, quarter stick firecrackers do not contain nitroglycerin as dynamite does, and have far less explosive power.
In the United States, quarter sticks and similar large firecrackers are illegal to manufacture or possess without an ATF High Explosives Manufacturing License.
They are sometimes colloquially known as M-1000s.