The 1591USGY is an economy, general purpose ABS plastic enclosure in light gray, measuring 120 x 120 x 59 mm (4.72 x 4.72 x 2.32 in). It is aimed at designers and builders who want a square project box with integral card guides for vertical printed circuit board mounting, where a flame retardant material is not required. At 59 mm deep it is a lower-profile square case, suited to boards and assemblies that do not need the extra height of the 94 mm 1591V size.

This economy version is molded from general purpose plastic (GPABS) with a UL94 HB flame rating and is not flame retardant; the flame retardant equivalent in the same colour is 1591UGY. The enclosure is designed to meet IP54, and lap joint construction helps keep out dust and splashing water. Light Gray enclosures in the 1591 series come with standard nickel finish screws.

Inside dimensions are 113.54 x 113.54 mm (4.470 x 4.470 in) with an inside height of 54.90 mm (2.161 in). Card guides molded into all side walls accept 1.5 mm (0.062 in) boards and provide a guide height of 49.90 mm (1.965 in). For horizontal board mounting, 1591Z PC board card adaptors can be used.

The purchased assembly includes box, lid and 4 cover screws. On economy versions the lid is assembled with #4 self-tapping screws into fully plastic posts, with a recommended torque of 42-57 ozf.in (30-40 cN.m); replacement screws are 1591TS100 (silver) or 1591TS100BK (black). A 1591UC clear polycarbonate lid fits this size, and the 1591USGY can be factory modified by milling, drilling or printing.