Featherboards are also useful for edge jointing, and making moulding on router tables. Columnar jointing is not limited to rhyolite formations. Columnar jointing occurs when certain types of lava contract while cooling. It displays columnar jointing formed as the lava cooled. Columnar jointing is also known as either "columnar structure", "prismatic joints", or "prismatic jointing". For this task, after jointing one face, a thickness planer is used. It contains columnar jointing units that are usually in diameter. Other tubes have concentric and radial jointing features. Rare cases of columnar jointing have also been reported from sedimentary strata. Compared with other examples of columnar jointing, the Postpile has more hexagonal columns. Pillows typically consist of a fine-grained core with a glassy crust and have radial jointing. Hawks are also used to hold joint compound for tape and jointing. This type of jointing is typical of thick lava flows and shallow dikes and sills. They require special techniques for jointing and terminating, see High-voltage cable. The rock is highly compressed and contains numerous fracture lines and jointing.