2 Dolla cog
Yeah, they're really only two bucks!
These definitely aren't the best cogs in the world but they're made of steel and will suit your needs if you're experimenting with gear ratios on a budget or want to keep a few in your pockets to chuck at shitty tweakers.
• standard 1.370" x 24tpi English threading
• size: 16t, 17t
• chrome plated