Screws and bolts are similar to each other and would qualify as one, but Govt. tariffs and specifications make the case different. Bolts need to correspond to certain sizes like M and MJ. There is no such classification for screws. Both of them are fastening materials.

While hex bolts have greater fortitude and are used to tighten bridges, machine screws are generally used to plug in holes. There are different screws and bolts for different uses. Plastered walls are fixed with drywall screws. Wood is taken care of with wood screws. Then there are concrete and metal screws. They differ from .75 cm to even 3 cm according to use. To reach typical spaces, toggle blot is used while to fix carriages, carriage bolt with customized shanks are used.

Generally, the sizes and thread types of these screws or bolt defines its actual use, for practical uses there can be intermix of screws.