Buyers and maintenance engineers may search for this model using names such as Sigma M56, SigmaM56, Sigma M-56, API Sigma M56, API Schmidt Sigma M56, Schmidt Sigma M56, Sigma 56, and related API Heat Transfer Sigma references. Sigma M55, Sigma M66, and Sigma M96 may also appear in the same product-family searches, but they are separate models and should not be assumed interchangeable. Senovis PHE can help confirm the correct model from the nameplate, plate profile, gasket shape, dimensions, or original Part Number.