MB-4 Polyethylene Water Meter Box Approximate Measurements 18" Diameter x 18" Length Proven Service The MB-4 has a variety of applications for different sized meter sets. The 18" depth is used in shallow to moderate frost lines. The circular design allows for an equal distribution of force and as a result this box can withstand considerable load pressure. The box tapers from top to bottom so it would be easily adjusted to grade. Item #76-77 Proven Processing Our structural foam molding process allows our parts to have a cellular foamed core surrounded by integral skins. The process gives our products high strength-to-weight ratio making it have greater rigidity than solid parts of the same material and of equal weight.