Since RS dont manufacture anything, there must be someone else stocks the same part... 5min with Google finds http://www.qtcgears.com/RFQ/default....les/khk144.htm Look at SR2-500 third section down, identical spec with DXF/PDF/DWG files. These are not 'machined ends' (thats elsewhere in the catalog) so i suspect these don't butt, you will have to machine the ends. Indeed you can tell this from the measurements. Circular pitch = Module * pi = 2 * 3.1416 = 6.2832mm so 80 teeth would be 80 * 6.2832 = 502.656mm which is the length of the 'machined ends' version. These have a length of 505mm!