The Brunson 803-C Invar Kits are designed as multipurpose kits. They are often used as scale extension tools – precisely extending the range of standard optical tooling scales for accurate measurement of larger dimensions, or to access previously unreachable points.  Invar tubing is great for metrology because it has such a very low coefficient of thermal expansion, which effectively eliminates changes in length due to handling or environmental changes. This is particularly beneficial when measuring a system in its "hot" or running state.
 
Data Sheet