Thomas & Betts LN-501 Steel City Conduit Locknut Brand: Thomas & Betts. Part Number: LN-501. Steel City Conduit Locknut, Non-Metallic, 1/2 in, For Use With: Rigid/IMC Conduit, Plastic. Additional Description: TB -LN-501 1/2 INCH PLASTIC LOCKNUT - BULK. Catalog Description: Locknut, 1/2 Inch, for Use with Rigid/IMC Conduit, Plastic..