Wide range of ID measurements by combining extension rods (pipes) and anvils with the micrometer head. - See more at: http://ecatalog.mitutoyo.com/Tubular-Inside-Micrometers-Series-137-Extension-Rod-TypeSeries-139-Extension-Pipe-typeSeries-140-Extension-Pipe-Type-C1513.aspx#sthash.JmIFwkpb.dpuf