This is a cottered crank. These were on old bikes, and at the co-op are mostly found on cheaper old bikes. If you are sorting a cottered crank, it has come off of a bike. Cottered cranks are almost never put back onto bikes. Notice the round hole at the end of the arm which is in the middle of the geared ring.
This is a cheap mountain crank. The chainrings are steel and they are riveted together. They look sort of like they might be bolted using allen bolts, but an inspection of the back of the crank lets you know that they are not.
This is a one piece crank with no chainrings. These are also known as American cranks. Notice how the piece includes both left and right crankarms and the bottom bracket spindle.
Here is an American BMX crank with a chainwheel on it.
Here is a typical American crank you might see at the co-op. It is from a cheap old bike and has the steel rings and chainguard still attached.
|Ball Bearings • Brakes (Caliper Brakes, Cantilever Brakes & Disc Brakes) • Brake Levers • Chainrings • Chains • Cranks|
|Derailers (Front & Rear) • Forks • Frame • Front Derailers • Handlebars • Hubs • Pedals • Quick Release|
|Rim • Seatposts • Seats • Shifters • Skewer • Spokes • Stems • Tires • Tubes • Wheels|