Carhartt dark blue coveralls, XL size, marked 'FR' for 'flame resistant'. Reference #RN14806, made in Mexico from US components. "44 Regular" size, like an XL.
Fantastic piece, rare.
 
Zip fastening,  2 chest flap pockets, 2 hip pockets, 2 back pockets and too pocket on the leg.
88% cotton & 12% nylon.