A Franklin Miller grinder installed in an Openchannelflow fiberglass manhole.  Site changes meant that the manhole had to be moved to a location where the line was deeper than orginally intended. This necessitate an extension to make the manhole deeper. The joint between the original (base) manhole secition and the extension can be see where the bolts extend in the manhole.  

Height changes, while rare, are occasionally called for.  For those instances, Openchannelflow has manhole extension and top style change kits available.