This a Barbron aluminum mesh flame arrestor.
Standard size for Holley is 5 3/4 inches in diameter, 3 inches tall and the opening is 5 1/8 inches. Fittings include: 1/4 inch, and no fitting.
Standard size for most 4 barrel carburetors like Holley, Carter, Edelbrock, Rochester and most other carbs with a 5 inch opening. It is 5 3/4 wide, 3 3/4 inches tall and fittings include: 1/4 inch fuel pump fitting, 1/2 inch breather fitting, or 5/8 breather fitting.
Coast Guard approved.