Bike wheel spokes can be made of steel or stainless steel. The most common diameters are 1.8 mm 2 mm or 2.3 mm for mountain bike wheels. Their colors can be black or steel color. For a 700C diameter wheel, you will generally need 32, 36 or 40 spokes. A broken spoke is easy to change, you have to unscrew the nipple from the rim and remove it. The spokes can be loosened, to tighten them, use a spoke wrench.