What is my wall made of and how should I hang a 50lb mirror?
Stud, if you can
While there are plenty of fasteners that claim to be rated for &quot;x&quot; lbs., if you can mount using screws into studs that is generally the best thing to do. Screws into studs can typically hold hundreds of lbs., like kitchen cabinets full of dishes.
Studs are usually 16&quot; apart in 20th century US housing. So once you find one stud you can usually find another easily. Drill a pilot hole where you think you have a stud and if you &quot;break through&quot; after ~ 1&quot; then keep searching.