Block 13 : Metal case enclosing one or more sheaves to facilitate a change of direction of a rope, or to gain mechanical advantage in transmission of power through a rope
Ministry of Business, Innovation and Employment, Glossary of terms and acronyms, Wellington, New Zealand 2010. http://wwwsosh.govt.nz/resources/glossary-u.shtml, (Occupn Hlth and Sfty - Brit) {530}