Razor Blades

Double edge blades fit any standard double edge safety razor. Single edge blades suit shavettes and single edge razors; each listing says which razors it fits.

Sharpness: mild blades such as Derby Extra and Astra Superior Platinum forgive a shaky angle. Sharp blades such as Feather Hi-Stainless cut coarse beards more easily but punish pressure.
Coating: platinum and PTFE coatings make a blade feel smoother on the first shaves. Uncoated blades feel crisper.
Finding your blade: the same blade feels different in different razors and on different beards. A blade sample kit is the cheapest way to find yours.