http://www.engineeringtoolbox.com/contract-types-d_925.html# Engineeringtoolbox. http://www.engineeringtoolbox.com/contract-types-d_925.html# http://www.engineeringtoolbox.com/contract-types-d_925.html# http://www.engineeringtoolbox.com/contract-types-d_925.html# Engineering ToolBox: Contract Types