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Amazon [amazon.com] has CRAFTSMAN Carbon Steel 3/4-in Utility Razor Blade (10-Pack) | CMHT11700X for $1.71. Shipping is free w/ Prime or on $35+.

Product Description from Amazon:BLADE SHARPNESS: Induction hardened blade for long lasting sharpness
DURABILITY: Blade stays 3 times sharper longer than traditional carbon steel blades
Fits most standard utility knives
10 Pack