In the past, Square D has used the term "mill duty rated" to describe our Nema 12 safety switches that were provided with factory installed copper lugs. The current series switch does not come with copper lugs as standard. Copper lug kits are available for field or factory installation. For factory installation, add suffix SLC to the catalog number. Lexington will provide a letter if requested, self certifying the Nema Type 12 switch with copper lugs as Mill Duty.