Bicycle manufacturers design and produce bicycles for leisure, commuting, sport and specialist uses. Their work may include developing frame geometry, selecting materials such as aluminium, steel, carbon fibre or titanium, and making or sourcing frames, forks and other components. Some businesses carry out the full production process, while others assemble finished bicycles from parts supplied by specialist manufacturers. Products can include road, mountain, hybrid, touring, folding, children's and cargo bicycles, as well as electric bicycles. Manufacturers may offer different frame sizes, component specifications and models for particular riding conditions. Services can include custom frame building, made-to-measure designs, bicycle assembly, quality checks and testing. Some also supply replacement frames or components, or provide technical support and warranty servicing through their own facilities or bicycle retailers.