This is a vintage pair of mens (unisex) work overalls or coveralls, probably from the 1950s. Unlabeled, the metal button at the neck is stamped SANFORIZED. Made of cotton 'salt and pepper' denim in a greenish-gray color, these have long sleeves and multiple pockets. Remarkably dirty from who-knows-how long ago, these are sold AS FOUND... it's killing me to not wash them but I never wash vintage workwear.
 
Aside from being grimy, they're in good condition with no noted flaws. The Talon brass fly zipper works great, the hidden snaps at the pocket flap, wrist and the brass snap at the neck/collar works great.
 
Probably a modern size large-ish to XL depending on whether you're wearing them with or without clothes underneath. These coveralls are marked chest 42" inseam 33"- but it's old with different sizing than modern clothing AND it's probably been shrunk in the wash. Here's the actual garment measurements-
 
Pit to pit- 25"
Waist- 40" around
Front neck to crotch- 30"
Inseam- 31"
Sleeve length- 25"