; v angleščini
*[http://www.lara.com/reviews/screwtypes.htm Lara Tools screw types] -
specialty tool dealer documents more than two dozen different screw heads, along with their drivers
*[http://www.boltscience.com Bolt Science] -
commercial site provides detailed introduction to bolting, including software programs for selecting a particular fastener and for determining the stress on a bolt.
Bolt-Grade-Chart.aspx boltdepot.com] Bolt Grade Markings and Strength Chart American & Metric