Square D B40.0 Thermal Unit Brand: Square D. Part Number: B40.0. Square D Thermal Unit, Melting Alloy, 21.5 to 35.3 A Full Load, Standard Trip, 5 in L x 3.5 in W x 0.8 in H, Plug-In Mount, 40 deg C. Additional Description: SQD -B40.0 THERMAL UNIT. Catalog Description: Thermal Unit, Type S, Type B, melting alloy, Class 20..